Hydraulic Fitting Size Chart: Complete Identification Guide from PLYET Industrial
Key Takeaways
- A hydraulic fitting size chart helps match hose, tube, and port threads (NPT/NPTF, BSP, JIC, ORB, ORFS, metric) to the correct size and pressure rating—this guide walks through how to read them step by step.
- To identify the standard size of a hydraulic fitting, one must determine its Dash Size, thread type, and seat angle.
- Misidentifying thread type or size causes leaks, galling, and costly downtime; the sections below show how to measure outside diameter, pitch, and seat angle correctly.
- PLYET Industrial focuses on fittings buyers actually use in real fluid power systems—construction, agriculture, mobile equipment, and factory hydraulics.
- An FAQ at the end answers common questions about mixing standards and upgrading older equipment to higher-pressure connections.
Introduction: Why Hydraulic Fitting Size Charts Matter in Real Systems
Most hydraulic downtime PLYET sees in 2026 still traces back to mismatched fittings, misread thread sizes, or mixing incompatible standards. A hydraulic fitting size chart is a practical reference listing thread type, nominal size, threads per inch or pitch, seat angle, and typical pressure ranges. This article is written from PLYET Industrial’s perspective as a supplier of hose fittings, adapters, and hydraulic fittings for OEMs and maintenance teams. The following sections cover NPT/NPTF, SAE connections (JIC, ORB, ORFS), BSP, DIN/metric, JIS, and instrumentation fittings—always coming back to practical chart use.
How to Use a Hydraulic Fitting Size Chart
Before diving into specific thread families, you must know how to measure and read size chart columns. Specifications vary by thread type, sealing method, and pressure rating.
PLYET’s fitting size charts include:
- Thread type/standard (NPTF, BSPP, JIC, etc.)
- Nominal Size and Dash Size
- Major/minor diameter in mm and inch measurements
- Pitch (metric) or TPI (threads per inch)
- Seat angle
- Recommended pressure range
- Material options (carbon steel, stainless, brass)
The Dash Size refers to the nominal size of the hose or fitting in 1/16-inch increments. Hydraulic fitting sizes are commonly expressed using dash numbers, where each unit represents 1/16 of an inch. Dash sizes commonly include -4 (1/4), -6 (3/8), -8 (1/2), -12 (3/4), and -16 (1). For metric fittings, dash sizes are not used; they are identified by the actual outside diameter.
To determine the correct size of a hydraulic fitting, one should identify the connection type, measure the thread diameter, and determine the thread pitch. Use a caliper for the outside diameter on male threads and the inside diameter on female connections. A thread pitch gauge identifies metric pitch or TPI for inch threads—avoid eyeballing.
Cross-check at least three data points—OD, pitch/TPI, and seat style—before selecting adapters or hose ends.
Hydraulic Fitting Size Chart from PLYET Industrial Supply
Hydraulic Dash Size Reference Chart
Dash sizes are commonly used for many hydraulic hose fittings and adapters. Each dash number represents 1/16 of an inch.
| Dash Size | Fractional Size | Decimal Size | Common Hose/Tube Size |
|---|---|---|---|
| -2 | 1/8" | 0.125" | Small instrumentation / pilot lines |
| -3 | 3/16" | 0.188" | Light hydraulic / brake / fuel |
| -4 | 1/4" | 0.250" | Common hydraulic hose size |
| -5 | 5/16" | 0.313" | Less common intermediate size |
| -6 | 3/8" | 0.375" | Common hydraulic hose size |
| -8 | 1/2" | 0.500" | Common hydraulic hose size |
| -10 | 5/8" | 0.625" | Medium hydraulic lines |
| -12 | 3/4" | 0.750" | High-flow hydraulic lines |
| -16 | 1" | 1.000" | Large hydraulic lines |
| -20 | 1-1/4" | 1.250" | Large industrial hydraulics |
| -24 | 1-1/2" | 1.500" | High-flow hydraulic systems |
| -32 | 2" | 2.000" |
Very large hydraulic systems |
National Pipe Threads: NPT and NPTF in Hydraulic Service
Pipe threads remain common on legacy hydraulic equipment in North America, though PLYET recommends modern O-ring connections for new designs. Hydraulic fittings are standardized based on thread type and diameter, with common types including JIC 37° Flare, NPT/NPTF, ORFS, and BSP.
National Pipe Tapered (NPT) is the general-purpose tapered thread for fluids and gases. Size charts list nominal size, major OD, TPI, and pressure range. For example, 1/4-18 NPTF shows approximately 0.54 inch OD, 18 TPI, suitable for low to medium pressure ports.
NPTF fittings create a tight, “dry seal” through thread deformation. NPTF fittings feature both male and female threads that form this seal, although they are not recommended for hydraulic systems by the NFPA due to potential leakage issues. PLYET uses size charts mainly to help retrofit older NPTF ports to ORB or ORFS via adapters. See NPT vs. NPTF for more detailed explanation.
NPT / NPTF Hydraulic Fitting Size Chart
Connection type: Tapered pipe thread
Seal method: Thread interference; NPT typically uses sealant, NPTF is dryseal
Common use: Older hydraulic equipment, pipe adapters, legacy ports
Important note: NPT and BSPT may look similar but are not interchangeable because the thread angle and pitch differ. Tapered threads should be identified carefully before replacement.
| Nominal Pipe Size | Common Dash Equivalent | Male Thread OD Approx. | Threads Per Inch | Thread Type | Seal Style |
|---|---|---|---|---|---|
| 1/16" | -1 | 0.312" | 27 | NPT / NPTF | Tapered thread |
| 1/8" | -2 | 0.405" | 27 | NPT / NPTF | Tapered thread |
| 1/4" | -4 | 0.540" | 18 | NPT / NPTF | Tapered thread |
| 3/8" | -6 | 0.675" | 18 | NPT / NPTF | Tapered thread |
| 1/2" | -8 | 0.840" | 14 | NPT / NPTF | Tapered thread |
| 3/4" | -12 | 1.050" | 14 | NPT / NPTF | Tapered thread |
| 1" | -16 | 1.315" | 11.5 | NPT / NPTF | Tapered thread |
| 1-1/4" | -20 | 1.660" | 11.5 | NPT / NPTF | Tapered thread |
| 1-1/2" | -24 | 1.900" | 11.5 | NPT / NPTF | Tapered thread |
| 2" | -32 | 2.375" | 11.5 | NPT / NPTF | Tapered thread |
National Pipe Straight Mechanical (NPSM)
NPSM is a straight thread with a 30° seat, often found as a swivel female connection on hose assemblies in North American fluid power systems. PLYET’s NPSM charts list nominal pipe size, major thread diameter, TPI, and the 30° seat style.
The mechanical seal forms between the 30° internal chamfer on the male end and the inverted 30° seat on the female port—not on the threads themselves. NPSM female swivels can mate with chamfered male NPTF, but PLYET recommends matched components for higher pressures.
Field differentiation from BSPP: check TPI count and seat shape in the chart before ordering.
NPSM Hydraulic Fitting Size Chart
Connection type: Straight pipe thread
Seal method: 30° mechanical seat, not the threads
Common use: Swivel female hose ends and North American hydraulic hose assemblies
| Nominal Pipe Size | Common Dash Equivalent | Male Thread OD Approx. | Threads Per Inch | Seat Angle | Seal Style |
|---|---|---|---|---|---|
| 1/8" | -2 | 0.405" | 27 | 30° | Mechanical seat |
| 1/4" | -4 | 0.540" | 18 | 30° | Mechanical seat |
| 3/8" | -6 | 0.675" | 18 | 30° | Mechanical seat |
| 1/2" | -8 | 0.840" | 14 | 30° | Mechanical seat |
| 3/4" | -12 | 1.050" | 14 | 30° | Mechanical seat |
| 1" | -16 | 1.315" | 11.5 | 30° | Mechanical seat |
| 1-1/4" | -20 | 1.660" | 11.5 | 30° | Mechanical seat |
| 1-1/2" | -24 | 1.900" | 11.5 | 30° | Mechanical seat |
| 2" | -32 | 2.375" | 11.5 | 30° | Mechanical seat |
SAE and JIC Flare Fittings in Hydraulic Systems
These straight-thread connections use metal angled surfaces at flared tube ends. PLYET supports them extensively for mobile hydraulics and industrial equipment. Common hydraulic fittings are identified by their seat angle, and similar fittings may have different angles.
Size charts group by standard: SAE J514 JIC 37 flare, SAE J512 45° flare, and SAE inverted flare. Charts include tube OD, thread size, seat angle, and maximum working pressure.
JIC 37° Flare (SAE J514)
JIC fittings, commonly used in hydraulic systems, feature a 37° flare sealing surface and straight United National Fine (UNF) threads, making them a popular choice in Europe. JIC fittings have 37° flare connectors with both male and female parts featuring a 37° flare seat and straight threads, providing a mechanical bond.
Size charts show tube outside diameter, thread size (e.g., 9/16-18 for -6 dash), and pressure ratings up to 6000-9000 psi depending on tube size and metal material.
Common sizes for JIC fittings include: 1/4” hose with 9/16” JIC, 3/8” hose with 9/16” or 3/4” JIC, 1/2” hose with 7/8” JIC, 3/4” hose with 1.1/16” JIC, and 1” hose with 1.5/16” JIC.
This universal sizing system applies across most American thread types like JIC, NPT, and ORFS. Use OD and thread size together to avoid confusion with SAE 45° flare fittings.
JIC 37° Flare Hydraulic Fitting Size Chart
Standard: SAE J514
Connection type: Straight UNF thread with 37° flare
Seal method: Metal-to-metal 37° flare seat
Common use: Mobile hydraulics, industrial equipment, agricultural equipment
| Dash Size | Tube OD | Thread Size | Male Thread OD Approx. | Threads Per Inch | Seat Angle | Seal Style |
|---|---|---|---|---|---|---|
| -2 | 1/8" | 5/16-24 | 0.313" | 24 | 37° | Flare seat |
| -3 | 3/16" | 3/8-24 | 0.375" | 24 | 37° | Flare seat |
| -4 | 1/4" | 7/16-20 | 0.438" | 20 | 37° | Flare seat |
| -5 | 5/16" | 1/2-20 | 0.500" | 20 | 37° | Flare seat |
| -6 | 3/8" | 9/16-18 | 0.563" | 18 | 37° | Flare seat |
| -8 | 1/2" | 3/4-16 | 0.750" | 16 | 37° | Flare seat |
| -10 | 5/8" | 7/8-14 | 0.875" | 14 | 37° | Flare seat |
| -12 | 3/4" | 1-1/16-12 | 1.063" | 12 | 37° | Flare seat |
| -14 | 7/8" | 1-3/16-12 | 1.188" | 12 | 37° | Flare seat |
| -16 | 1" | 1-5/16-12 | 1.313" | 12 | 37° | Flare seat |
| -20 | 1-1/4" | 1-5/8-12 | 1.625" | 12 | 37° | Flare seat |
| -24 | 1-1/2" | 1-7/8-12 | 1.875" | 12 | 37° | Flare seat |
| -32 | 2" | 2-1/2-12 | 2.500" | 12 | 37° | Flare seat |
SAE 45° Flare (SAE J512)
SAE 45° flare fittings serve low-pressure applications—fuel lines, refrigerant circuits, automotive systems. Charts list tubing OD, thread size, and 45° seat designation, typically brass construction.
Even when the thread size matches JIC 37°, the 45° flare angle is not interchangeable.
Mixing them causes persistent leaks. Always check both angle and diameter on the chart.
SAE 45° Flare Fitting Size Chart
Standard: SAE J512
Connection type: Straight thread with 45° flare
Seal method: Metal-to-metal 45° flare
Common use: Fuel lines, refrigerant lines, automotive systems, low-pressure applications
Important note: SAE 45° flare is not interchangeable with JIC 37° flare, even when the thread size looks similar.
| Tube OD | Thread Size | Male Thread OD Approx. | Threads Per Inch | Seat Angle | Common Material |
|---|---|---|---|---|---|
| 1/8" | 5/16-24 | 0.313" | 24 | 45° | Brass / steel |
| 3/16" | 3/8-24 | 0.375" | 24 | 45° | Brass / steel |
| 1/4" | 7/16-20 | 0.438" | 20 | 45° | Brass / steel |
| 5/16" | 1/2-20 | 0.500" | 20 | 45° | Brass / steel |
| 3/8" | 5/8-18 | 0.625" | 18 | 45° | Brass / steel |
| 1/2" | 3/4-16 | 0.750" | 16 | 45° | Brass / steel |
| 5/8" | 7/8-14 | 0.875" | 14 | 45° | Brass / steel |
| 3/4" | 1-1/16-14 | 1.063" | 14 | 45° | Brass / steel |
SAE Inverted Flare (SAE J512)
SAE inverted flare fittings were historically popular in automotive brake and power steering systems, using an internal flare and a 42° or 45° geometry. Charts indicate nut thread size, tube OD, and seat angle.
The male connector has the seat, and the female has the internal flare. While not common for new industrial hydraulics, PLYET stocks these for retrofit on older machinery.
SAE Inverted Flare Fitting Size Chart
Standard: SAE J512
Connection type: Inverted flare
Seal method: Internal flare seat
Common use: Automotive brake, power steering, fuel, and older equipment systems
| Tube OD | Thread Size | Male Thread OD Approx. | Threads Per Inch | Seat Style | Common Use |
|---|---|---|---|---|---|
| 3/16" | 3/8-24 | 0.375" | 24 | Inverted flare | Brake / light hydraulic |
| 1/4" | 7/16-24 | 0.438" | 24 | Inverted flare | Automotive / retrofit |
| 5/16" | 1/2-20 | 0.500" | 20 | Inverted flare | Fuel / steering |
| 3/8" | 5/8-18 | 0.625" | 18 | Inverted flare | Steering / fuel |
| 1/2" | 3/4-18 | 0.750" | 18 | Inverted flare | Larger fluid lines |
| 5/8" | 7/8-18 | 0.875" | 18 | Inverted flare | Larger fluid lines |
SAE O-Ring Ports: ORB and ORFS
O-ring face seal and O-ring boss connections are the modern workhorses for high-pressure hydraulic systems that PLYET recommends for leak-sensitive applications. The seal is elastomeric rather than metal-to-metal.
SAE J1926 O-Ring Boss (ORB)
ORB fittings utilize an O-ring and straight threads, where the seal is formed when the O-ring fits snugly into a chamfer on the female connector, ensuring a robust mechanical bond. ORB fittings feature a female port with a sealing face, chamfer, and straight threads, while the male connector includes an O-ring and straight threads, commonly used in high-pressure hydraulic systems.
Size charts list nominal thread size (7/16-20 through 1 7/8-12), O-ring cross-section, and port counterbore dimensions. ORB is preferred over NPTF because it is less sensitive to assembly technique.
SAE ORB O-Ring Boss Fitting Size Chart
Standard: SAE J1926
Connection type: Straight UN/UNF thread with O-ring
Seal method: O-ring seals against port chamfer
Common use: High-pressure hydraulic ports, pumps, valves, manifolds
ORB fittings use straight threads and an O-ring near the hex to create the seal rather than relying on the threads themselves.
| Dash Size | Thread Size | Male Thread OD Approx. | Threads Per Inch | Seal Style | Common Use |
|---|---|---|---|---|---|
| -2 | 5/16-24 | 0.313" | 24 | O-ring boss | Small hydraulic ports |
| -3 | 3/8-24 | 0.375" | 24 | O-ring boss | Small hydraulic ports |
| -4 | 7/16-20 | 0.438" | 20 | O-ring boss | Common hydraulic ports |
| -5 | 1/2-20 | 0.500" | 20 | O-ring boss | Compact hydraulic ports |
| -6 | 9/16-18 | 0.563" | 18 | O-ring boss | Common hydraulic ports |
| -8 | 3/4-16 | 0.750" | 16 | O-ring boss | Pumps / valves |
| -10 | 7/8-14 | 0.875" | 14 | O-ring boss | Pumps / manifolds |
| -12 | 1-1/16-12 | 1.063" | 12 | O-ring boss | High-flow ports |
| -14 | 1-3/16-12 | 1.188" | 12 | O-ring boss | Large hydraulic ports |
| -16 | 1-5/16-12 | 1.313" | 12 | O-ring boss | Large hydraulic ports |
| -20 | 1-5/8-12 | 1.625" | 12 | O-ring boss | High-flow systems |
| -24 | 1-7/8-12 | 1.875" | 12 | O-ring boss | High-flow systems |
| -32 | 2-1/2-12 | 2.500" | 12 | O-ring boss | Very large systems |
O-Ring Face Seal (ORFS, SAE J1453)
ORFS fittings use a flat face with an O-ring on the male side, mating to a flat machined surface. O-Ring Face Seal (ORFS) fittings provide excellent leak protection by compressing an O-ring against a flat machined surface, suitable for applications up to 6000 psi.
The most commonly found sizes for ORFS fittings on hydraulic hoses are: 1/4” hose with 9/16” ORFS, 3/8” hose with 11/16” ORFS, 1/2” hose with 13/16” and 1” ORFS, 3/4” hose with 1.3/16” ORFS, and 1” hose with 1.7/16” ORFS.
ORFS is popular on excavators and skid steers where zero-leak requirements are strict. The ring face seal tolerates minor rotation during hose replacement better than flared seats.
ORFS O-Ring Face Seal Fitting Size Chart
Standard: SAE J1453
Connection type: Straight thread with flat sealing face
Seal method: O-ring compressed against flat face
Common use: High-pressure, leak-resistant hydraulic systems, excavators, skid steers, mobile equipment
| Dash Size | Tube OD | Thread Size | Male Thread OD Approx. | Threads Per Inch | Seal Style |
|---|---|---|---|---|---|
| -4 | 1/4" | 9/16-18 | 0.563" | 18 | Flat face O-ring |
| -6 | 3/8" | 11/16-16 | 0.688" | 16 | Flat face O-ring |
| -8 | 1/2" | 13/16-16 | 0.813" | 16 | Flat face O-ring |
| -10 | 5/8" | 1-14 | 1.000" | 14 | Flat face O-ring |
| -12 | 3/4" | 1-3/16-12 | 1.188" | 12 | Flat face O-ring |
| -16 | 1" | 1-7/16-12 | 1.438" | 12 | Flat face O-ring |
| -20 | 1-1/4" | 1-11/16-12 | 1.688" | 12 | Flat face O-ring |
| -24 | 1-1/2" | 2-12 | 2.000" | 12 | Flat face O-ring |
Metric and European Hydraulic Fittings
Metric threads (DIN 2353/ISO 8434, ISO 6149) dominate European and Asian-built machinery. Metric thread identification follows the designation ‘M’ followed by the nominal diameter and pitch in millimeters, such as M8 x 1.0 for fine pitch, with the absence of pitch indicating coarse pitch.
DIN 24° Cone and Metric Tube Fittings
DIN 24° cone fittings are standard across European hydraulics. Charts show tube OD (6, 8, 10, 12 mm, etc.), thread designation (M12x1.5, M18x1.5), and pressure series (LL, L, S).
Metric hydraulic fittings commonly follow the DIN 2353 standard, with sizes such as: 1/4” hose corresponding to 10L Metric, 3/8” hose to 12L Metric, 1/2” hose to 15L Metric, 3/4” hose to 22L Metric, and 1” hose to 28L Metric.
Identifying the correct series from the chart is critical—the same tube OD may use different thread sizes.
DIN 24° Metric Tube Fitting Size Chart
Standard: DIN 2353 / ISO 8434
Connection type: Metric straight thread with 24° cone
Seal method: 24° cone with cutting ring, bite-type sleeve, or O-ring cone
Common use: European hydraulic machinery, construction equipment, industrial systems
DIN Light Series — L Series
| Tube OD | Metric Thread | Pitch | Series | Seat Angle | Common Hose Equivalent |
|---|---|---|---|---|---|
| 6 mm | M12 x 1.5 | 1.5 mm | L | 24° | Small metric line |
| 8 mm | M14 x 1.5 | 1.5 mm | L | 24° | Small metric line |
| 10 mm | M16 x 1.5 | 1.5 mm | L | 24° | Approx. 1/4" |
| 12 mm | M18 x 1.5 | 1.5 mm | L | 24° | Approx. 3/8" |
| 15 mm | M22 x 1.5 | 1.5 mm | L | 24° | Approx. 1/2" |
| 18 mm | M26 x 1.5 | 1.5 mm | L | 24° | Medium line |
| 22 mm | M30 x 2.0 | 2.0 mm | L | 24° | Approx. 3/4" |
| 28 mm | M36 x 2.0 | 2.0 mm | L | 24° | Approx. 1" |
| 35 mm | M45 x 2.0 | 2.0 mm | L | 24° | Large metric line |
| 42 mm | M52 x 2.0 | 2.0 mm | L | 24° | Large metric line |
DIN Heavy Series — S Series
| Tube OD | Metric Thread | Pitch | Series | Seat Angle | Common Use |
|---|---|---|---|---|---|
| 6 mm | M14 x 1.5 | 1.5 mm | S | 24° | High-pressure small line |
| 8 mm | M16 x 1.5 | 1.5 mm | S | 24° | High-pressure small line |
| 10 mm | M18 x 1.5 | 1.5 mm | S | 24° | High-pressure small line |
| 12 mm | M20 x 1.5 | 1.5 mm | S | 24° | High-pressure hydraulic |
| 14 mm | M22 x 1.5 | 1.5 mm | S | 24° | High-pressure hydraulic |
| 16 mm | M24 x 1.5 | 1.5 mm | S | 24° | High-pressure hydraulic |
| 20 mm | M30 x 2.0 | 2.0 mm | S | 24° | High-pressure hydraulic |
| 25 mm | M36 x 2.0 | 2.0 mm | S | 24° | High-pressure hydraulic |
| 30 mm | M42 x 2.0 | 2.0 mm | S | 24° | Large high-pressure line |
| 38 mm | M52 x 2.0 | 2.0 mm | S | 24° | Large high-pressure line |
ISO 6149 Metric O-Ring Ports
ISO 6149 is the metric counterpart to SAE J1926 ORB, using straight metric threads and an O-ring in the port. Charts list metric thread size, port counterbore dimensions, and O-ring sizes.
ISO 6149 Metric O-Ring Port Size Chart
Standard: ISO 6149
Connection type: Metric straight thread with O-ring port
Seal method: O-ring seal in port
Common use: Metric hydraulic ports, European equipment, modern machinery
| Metric Thread | Pitch | Male Thread OD | Seal Style | Common Use |
|---|---|---|---|---|
| M8 x 1.0 | 1.0 mm | 8 mm | Metric O-ring port | Small port |
| M10 x 1.0 | 1.0 mm | 10 mm | Metric O-ring port | Small port |
| M12 x 1.5 | 1.5 mm | 12 mm | Metric O-ring port | Small hydraulic port |
| M14 x 1.5 | 1.5 mm | 14 mm | Metric O-ring port | Small hydraulic port |
| M16 x 1.5 | 1.5 mm | 16 mm | Metric O-ring port | Common hydraulic port |
| M18 x 1.5 | 1.5 mm | 18 mm | Metric O-ring port | Common hydraulic port |
| M20 x 1.5 | 1.5 mm | 20 mm | Metric O-ring port | Common hydraulic port |
| M22 x 1.5 | 1.5 mm | 22 mm | Metric O-ring port | Medium hydraulic port |
| M27 x 2.0 | 2.0 mm | 27 mm | Metric O-ring port | Medium hydraulic port |
| M30 x 2.0 | 2.0 mm | 30 mm | Metric O-ring port | Medium hydraulic port |
| M33 x 2.0 | 2.0 mm | 33 mm | Metric O-ring port | Large hydraulic port |
| M42 x 2.0 | 2.0 mm | 42 mm | Metric O-ring port | Large hydraulic port |
| M48 x 2.0 | 2.0 mm | 48 mm | Metric O-ring port | Large hydraulic port |
Komatsu and Chinese Metric Fittings
Komatsu and Chinese GB/JB fittings follow metric dimensions but may use 37° or 45° flare designs. PLYET’s charts tag these by OEM style and include thread designation, seat angle, and equipment category.
Komatsu / Chinese Metric Hydraulic Fitting Size Chart
Connection type: Metric thread, often 30°, 37°, or 45° flare depending on equipment style
Common use: Komatsu equipment, Chinese-built machinery, imported hydraulic systems
Important note: These can look similar to DIN or JIC fittings, but the thread pitch and seat angle may differ.
| Metric Thread | Pitch | Male Thread OD | Common Seat Style | Common Use |
|---|---|---|---|---|
| M14 x 1.5 | 1.5 mm | 14 mm | 30°, 37°, or 45° flare | Small equipment lines |
| M16 x 1.5 | 1.5 mm | 16 mm | 30°, 37°, or 45° flare | Small hydraulic lines |
| M18 x 1.5 | 1.5 mm | 18 mm | 30°, 37°, or 45° flare | Common hydraulic lines |
| M20 x 1.5 | 1.5 mm | 20 mm | 30°, 37°, or 45° flare | Common hydraulic lines |
| M22 x 1.5 | 1.5 mm | 22 mm | 30°, 37°, or 45° flare | Medium hydraulic lines |
| M24 x 1.5 | 1.5 mm | 24 mm | 30°, 37°, or 45° flare | Medium hydraulic lines |
| M27 x 1.5 | 1.5 mm | 27 mm | 30°, 37°, or 45° flare | Medium hydraulic lines |
| M30 x 1.5 | 1.5 mm | 30 mm | 30°, 37°, or 45° flare | Larger hydraulic lines |
| M33 x 1.5 | 1.5 mm | 33 mm | 30°, 37°, or 45° flare | Larger hydraulic lines |
| M36 x 1.5 | 1.5 mm | 36 mm | 30°, 37°, or 45° flare | Large hydraulic lines |
| M42 x 1.5 | 1.5 mm | 42 mm | 30°, 37°, or 45° flare | Large hydraulic lines |
British Standard Pipe Threads: BSPP and BSPT
British Standard Pipe (BSP) threads, also known as Whitworth threads, have a sealing angle of 60° and can be identified by measuring the outside diameter and the number of threads per inch. Charts distinguish between British Standard Pipe Parallel (BSPP, labeled G) and British Standard Pipe Tapered (BSPT, labeled R).
BSPT looks similar to NPTF but differs in thread angle and pitch—they are not interchangeable. BSPP male connectors seal via bonded washer, cone seat, or O-ring, depending on design. PLYET supplies adapters from BSP to JIC or ORFS for mixed-standard machines.
BSPP British Parallel Pipe Fitting Size Chart
Connection type: British Standard Pipe Parallel
Thread form: 55° Whitworth
Seal method: Bonded washer, O-ring, cone seat, or captive seal
Common use: European, British, and imported hydraulic equipment
| BSPP Size | Male Thread OD Approx. | Threads Per Inch | Thread Label | Thread Type | Common Seal Style |
|---|---|---|---|---|---|
| 1/8" | 0.383" | 28 | G 1/8 | Parallel | Washer / O-ring / cone |
| 1/4" | 0.518" | 19 | G 1/4 | Parallel | Washer / O-ring / cone |
| 3/8" | 0.656" | 19 | G 3/8 | Parallel | Washer / O-ring / cone |
| 1/2" | 0.825" | 14 | G 1/2 | Parallel | Washer / O-ring / cone |
| 5/8" | 0.902" | 14 | G 5/8 | Parallel | Washer / O-ring / cone |
| 3/4" | 1.041" | 14 | G 3/4 | Parallel | Washer / O-ring / cone |
| 1" | 1.309" | 11 | G 1 | Parallel | Washer / O-ring / cone |
| 1-1/4" | 1.650" | 11 | G 1-1/4 | Parallel | Washer / O-ring / cone |
| 1-1/2" | 1.882" | 11 | G 1-1/2 | Parallel | Washer / O-ring / cone |
| 2" | 2.347" | 11 | G 2 | Parallel | Washer / O-ring / cone |
BSPT British Tapered Pipe Fitting Size Chart
Connection type: British Standard Pipe Tapered
Thread form: 55° Whitworth
Seal method: Tapered thread seal, often with sealant
Common use: Imported machinery, older hydraulic systems, British-standard ports
| BSPT Size | Male Thread OD Approx. | Threads Per Inch | Thread Label | Thread Type | Seal Style |
|---|---|---|---|---|---|
| 1/8" | 0.383" | 28 | R 1/8 | Tapered | Thread seal |
| 1/4" | 0.518" | 19 | R 1/4 | Tapered | Thread seal |
| 3/8" | 0.656" | 19 | R 3/8 | Tapered | Thread seal |
| 1/2" | 0.825" | 14 | R 1/2 | Tapered | Thread seal |
| 3/4" | 1.041" | 14 | R 3/4 | Tapered | Thread seal |
| 1" | 1.309" | 11 | R 1 | Tapered | Thread seal |
| 1-1/4" | 1.650" | 11 | R 1-1/4 | Tapered | Thread seal |
| 1-1/2" | 1.882" | 11 | R 1-1/2 | Tapered | Thread seal |
| 2" | 2.347" | 11 | R 2 | Tapered | Thread seal |
German and Japanese Hydraulic Connections
German DIN and Japanese JIS connections appear on imported equipment that PLYET supports.
DIN 7631 and DIN 3852 Connections
DIN 7631 uses metric straight threads with a 60° recessed cone. DIN 3852 defines threaded ports with counterbore dimensions and sealing methods. PLYET stocks adapters bridging DIN to SAE/JIC.
DIN 7631 / DIN 3852 Metric Fitting Size Chart
Connection type: Metric straight thread
Seal method: 60° cone, bonded seal, O-ring, or port seal depending on style
Common use: German hydraulic equipment and imported machinery
| Metric Thread | Pitch | Male Thread OD | Common DIN Style | Seat / Seal Style |
|---|---|---|---|---|
| M10 x 1.0 | 1.0 mm | 10 mm | DIN metric | 60° cone / seal washer |
| M12 x 1.5 | 1.5 mm | 12 mm | DIN metric | 60° cone / seal washer |
| M14 x 1.5 | 1.5 mm | 14 mm | DIN metric | 60° cone / seal washer |
| M16 x 1.5 | 1.5 mm | 16 mm | DIN metric | 60° cone / seal washer |
| M18 x 1.5 | 1.5 mm | 18 mm | DIN metric | 60° cone / seal washer |
| M20 x 1.5 | 1.5 mm | 20 mm | DIN metric | 60° cone / seal washer |
| M22 x 1.5 | 1.5 mm | 22 mm | DIN metric | 60° cone / seal washer |
| M26 x 1.5 | 1.5 mm | 26 mm | DIN metric | 60° cone / seal washer |
| M30 x 1.5 | 1.5 mm | 30 mm | DIN metric | 60° cone / seal washer |
| M36 x 2.0 | 2.0 mm | 36 mm | DIN metric | 60° cone / seal washer |
| M42 x 2.0 | 2.0 mm | 42 mm | DIN metric | 60° cone / seal washer |
| M52 x 2.0 | 2.0 mm | 52 mm | DIN metric | 60° cone / seal washer |
JIS Threads and Flanges
JIS includes tapered pipe (PT), parallel threads with 30° seats, and 4-bolt flange connections. JIS 30° fittings resemble SAE 37° in profile but differ in thread pitch and seat angles. Charts specify code, bolt spacing, and working pressure for flange selection.
JIS Japanese Hydraulic Fitting Size Chart
Common types: JIS tapered pipe, JIS parallel pipe, JIS 30° flare, JIS flanges
Seal method: Thread seal, 30° seat, or flange seal
Common use: Japanese machinery, excavators, forklifts, imported hydraulic equipment
JIS Parallel / JIS 30° Seat
| JIS Size | Thread Type | Male Thread OD Approx. | Threads Per Inch | Seat Angle | Seal Style |
|---|---|---|---|---|---|
| 1/8" | BSPP/JIS Parallel | 0.383" | 28 | 30° | Seat seal |
| 1/4" | BSPP/JIS Parallel | 0.518" | 19 | 30° | Seat seal |
| 3/8" | BSPP/JIS Parallel | 0.656" | 19 | 30° | Seat seal |
| 1/2" | BSPP/JIS Parallel | 0.825" | 14 | 30° | Seat seal |
| 3/4" | BSPP/JIS Parallel | 1.041" | 14 | 30° | Seat seal |
| 1" | BSPP/JIS Parallel | 1.309" | 11 | 30° | Seat seal |
| 1-1/4" | BSPP/JIS Parallel | 1.650" | 11 | 30° | Seat seal |
| 1-1/2" | BSPP/JIS Parallel | 1.882" | 11 | 30° | Seat seal |
| 2" | BSPP/JIS Parallel | 2.347" | 11 | 30° | Seat seal |
JIS Tapered Pipe
| JIS Size | Thread Type | Male Thread OD Approx. | Threads Per Inch | Seal Style |
|---|---|---|---|---|
| 1/8" | PT / JIS Tapered | 0.383" | 28 | Tapered thread |
| 1/4" | PT / JIS Tapered | 0.518" | 19 | Tapered thread |
| 3/8" | PT / JIS Tapered | 0.656" | 19 | Tapered thread |
| 1/2" | PT / JIS Tapered | 0.825" | 14 | Tapered thread |
| 3/4" | PT / JIS Tapered | 1.041" | 14 | Tapered thread |
| 1" | PT / JIS Tapered | 1.309" | 11 | Tapered thread |
Instrumentation Fittings and UNEF Threads
Instrumentation fittings use tube OD as primary sizing (1/4”, 3/8”, or 6mm, 10mm) with UNEF threads. Double ferrule systems provide seal contact on a recessed cone surface while the back ferrule grips the tubing. These are frequently found in stainless steel for chemical applications.
Instrumentation / UNEF Fitting Size Chart
Connection type: Tube fitting with fine UNEF thread
Seal method: Ferrule compression or cone/ferrule seal
Common use: Stainless steel instrumentation, chemical, process, and control lines
| Tube OD | Common Thread Size | Thread Type | Male Thread OD Approx. | Threads Per Inch | Seal Style |
|---|---|---|---|---|---|
| 1/8" | 5/16-24 | UNF / UNEF style | 0.313" | 24 | Ferrule / compression |
| 3/16" | 3/8-24 | UNF / UNEF style | 0.375" | 24 | Ferrule / compression |
| 1/4" | 7/16-20 | UNF / UNEF style | 0.438" | 20 | Ferrule / compression |
| 5/16" | 1/2-20 | UNF / UNEF style | 0.500" | 20 | Ferrule / compression |
| 3/8" | 9/16-18 | UNF / UNEF style | 0.563" | 18 | Ferrule / compression |
| 1/2" | 3/4-16 | UNF / UNEF style | 0.750" | 16 | Ferrule / compression |
| 5/8" | 7/8-14 | UNF / UNEF style | 0.875" | 14 | Ferrule / compression |
| 3/4" | 1-1/16-12 | UNF / UNEF style | 1.063" | 12 | Ferrule / compression |
| 1" | 1-5/16-12 | UNF / UNEF style | 1.313" | 12 | Ferrule / compression |
Hydraulic Fitting Size Chart in Practice
PLYET engineers use size charts following this workflow: measure OD and pitch, identify thread family, confirm seat angle or groove configuration, check working pressure versus system pressure, then select the fitting or adapter.
This approach prevents common pitfalls like mixing near-identical thread types or undersizing fittings on high-pressure lines. For replacing a hose on a 300-bar excavator, chart-based identification ensures the correct ORFS connection the first time.
Quick Hydraulic Fitting Identification Chart
| Fitting Type | Thread Style | Seal Location | Seat / Seal Angle | Common Identifier |
|---|---|---|---|---|
| NPT | Tapered pipe | Threads | 60° thread form | Tapered thread, sealant used |
| NPTF | Tapered pipe | Threads | 60° thread form | Dryseal tapered thread |
| NPSM | Straight pipe | 30° seat | 30° | Female swivel, straight thread |
| JIC | Straight UNF | Flare seat | 37° | SAE J514, metal-to-metal flare |
| SAE 45° | Straight UNF | Flare seat | 45° | Brass/automotive style |
| SAE Inverted Flare | Straight UNF | Internal flare | 42°/45° | Automotive/older systems |
| ORB | Straight UNF | O-ring at port | O-ring | O-ring near hex |
| ORFS | Straight thread | Flat face O-ring | Flat face | Male has O-ring groove on face |
| BSPP | Parallel pipe | Washer/O-ring/cone | Varies | G thread designation |
| BSPT | Tapered pipe | Threads | 55° thread form | R thread designation |
| DIN 24° | Metric straight | 24° cone | 24° | L or S series |
| ISO 6149 | Metric straight | O-ring port | O-ring | Metric O-ring port |
| DIN 7631 | Metric straight | Cone/washer | 60° cone | German hydraulic connection |
| JIS 30° | BSP-style parallel | 30° seat | 30° | Japanese equipment |
| JIS Tapered | BSP-style tapered | Threads | 55° thread form | PT thread |
| Instrumentation | UNF/UNEF or metric | Ferrule | Compression | Tube OD sizing |
FAQ: Hydraulic Fitting Size Charts and Identification
How do I quickly tell whether a fitting is metric or inch-based?
Measure thread OD with a caliper and check pitch. If the distance between threads matches a whole millimeter (1.5mm, 2.0mm), it is likely metric. If you get fractional inch TPI (18, 14, 11.5), it is inch-based. PLYET’s charts group these separately for quick reference.
Can I safely mix NPTF, BSPT, and similar tapered threads?
PLYET does not recommend mixing NPTF and BSPT even if they hand-thread together. The thread angle and pitch differ, causing leaks under pressure. Use properly matched adapters from the chart instead.
When should I upgrade from flare fittings to ORFS or ORB?
Upgrade when recurring leaks occur at flare connections, when system pressure has increased, or during equipment rebuilds. Size charts help identify existing flare thread size and select compatible O-ring adapters.
How do I use a size chart if my fitting is damaged?
Take measurements from the least-damaged portion and, where possible, measure a matching undamaged port on the same machine. Contact PLYET with photos and partial measurements for assistance.
Do PLYET charts cover torque values?
Core size charts focus on dimensions and thread identification. Recommended assembly torques are provided in separate tables by thread size and material—available upon request for critical ORB and ORFS connections.
