Thread Identification

Identifying Threads

Accurate identification of ports and connectors in fluid piping systems is necessary before the correct hose, tube, or adapter fitting can be selected and installed. With the aid of our resources, measurement and identification can become an easy process.

How to ID

Download the guide

For a more detailed listing of thread types, or for additional reference, please download our guide to identify threads on the go or whenever convenient to you!

Download

Required Tools

Before you begin, please make sure to have the proper tools available. A seat angle gauge, thread pitch gauge, and an ID/OD caliper are necessary to make accurate measurements of commonly used connectors. Mid-State can provide these tools in one unit upon request.

Thread ID/OD Caliper

caliper

Seat Angle Gauge

angle gauge

Thread Pitch Gauge

thread pitch

Identification in three easy steps:

The easiest way to identify thread types is by visually comparing your part with the pictures below, and then taking measurements of the thread ID/OD, threads per inch, and seat angles as appropriate. Compare measurements to the accompanying charts to identify the correct size.

1

Thread Diameter

Using an ID/OD caliper, measure the outside diameter of the male threads, or inside diameter of female threads and match results to the accompanying chart. Please note, results may vary if the caliper arms do not sit flush against the threads, or if the connection is worn from service.

2

Seat Angle

If the port connection is angled, use a seal angle gauge to determine the proper seat angle. Female connections are usually measured by inserting the angle gauge into the connection and placing it on the sealing surface. If the connection and gauge are parallel, the correct angle has been determined. Male connections are usually measured by placing the gauge on the sealing surface. If the center-lines of the connection and gauge are parallel, the correct angle has been determined.

3

Threads Per Inch

Use a thread pitch gauge to determine the number of threads per inch or the distance between threads in metric connections. Place the gauge on the threads until the fit is snug, and then match the measurements to the accompanying chart.

Video Resources and Guides

Thread Pitch and Size- Courtesy of Swagelok
Fitting Identification- Courtesy of Brennan Industries.
Identifying Metric Threads- Courtesy of Adaptall, Inc.

Thread-Types

National Pipe Tapered Fuel (NPTF) is a connection widely used in fluid power systems, even though it is not recommended by the National Fluid Power Association for use in hydraulic applications. This thread is tapered and the seal takes place by deformation of the threads.

National Pipe Straight Mechanical (NPSM) is sometimes used in fluid power systems. The female half has a straight thread and an inverted 30° seat. The male is straight and has a 30° internal chamfer.

Male Pipe Drawing
Pipe
Female NPSM
Female PIpe Drawing

Measure thread diameter and subtract 1/4 inch to find the nominal pipe size.

Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/8
1/4
3/8
1/2
3/4
1
1-1/4
1-1/2
2
02
04
06
08
12
16
20
24
32
5/16-24
1/4-18
3/8-18
1/2-14
3/4-14
1-11.5
1-1/4 - 11.5
1-1/2 -11.5
2-11.5
.31
.54
.68
.84
1.05
1.32
1.66
1.90
2.38
.27
.49
.63
.77
.98
1.24
1.58
1.82
2.30
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread (subtract 1/4) and followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

SAE J514 37° JIC connection is very common in fluid power systems. Both the male and female halves of the connections have 37° seats. The seal takes place by establishing a line of contact between the male flare and the female cone seat. The threads hold the connection mechanically. Note – in sizes 02, 03, 04, 05, 08, and 10, the threads of SAE 37° and SAE 45° are the same, but the sealing surface angles are not.

Male JIC
JIC Cap
JIC Plug
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/8
02
5/16-24
.31
.27
3/16
03
3/8-24
.38
.34
1/4
04
7/16-20
.44
.39
5/16
05
1/2-20
.50
.45
3/8
06
9/16-18
.56
.51
1/2
08
3/4-16
.75
.69
5/8
10
7/8-14
.88
.81
3/4
12
1-1/16 -12
1.06
.98
7/8
14
1-13/16 -12
1.19
1.10
1
16
1-5/16 - 12
1.31
1.23
1-1/4
20
1-5/8 - 12
1.63
1.54
1-1/2
24
1-7/8 -12
1.88
1.79
2
32
2-1/2 - 12
2.50
2.42
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

SAE J514 Straight Thread O-Ring Boss connections are recommended by the N.F.P.A. for optimum leakage control in medium and high-pressure hydraulic systems. The male connector has a straight thread and an o-ring. The female port has a straight thread, a machined surface, and a chamfer designed to accept the o-ring. Sealing occurs when the o-ring is compressed into the chamfer. The threads hold the connection mechanically.

Male ORB
ORB Female
ORB Plug
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/8
02
5/16-24
.31
.27
3/16
03
3/8-24
.38
.34
1/4
04
7/16-20
.44
.39
5/16
05
1/2-20
.50
.45
3/8
06
9/16-18
.56
.51
1/2
08
3/4-16
.75
.69
5/8
10
7/8-14
.88
.81
3/4
12
1-1/16 -12
1.06
.98
7/8
14
1-13/16 -12
1.19
1.10
1
16
1-5/16 - 12
1.31
1.23
1-1/4
20
1-5/8 - 12
1.63
1.54
1-1/2
24
1-7/8 -12
1.88
1.79
2
32
2-1/2 - 12
2.50
2.42
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

SAE J1453 O-Ring Face Seal connections offer the very best leakage control available. The male connector has a straight thread and an o-ring in the face. The female has straight threads and a machined, flat face. The seal occurs by compressing the o-ring init the flat face of the female. The threads hold the connection mechanically.

Face Seal
Face Seal Cap
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/4
04
9/16-18
.56
.51
3/8
06
11/16-16
.69
.63
1/2
08
3/16-16
.82
.75
5/8
10
1-14
1.00
.93
3/4
12
1-3/16 - 12
1.19
1.11
1
16
1-7/16 - 12
1.44
1.36
1-1/4
20
1-11/16 -12
1.69
1.61
1-1/2
24
2-12
2.00
1.92
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

SAE J518 4-Bolt Flange is a connection widely used in fluid power systems. There are two pressure ratings. Code 61 is referred to as the standard series, while Code 62 is considered the 6000 psi series. The design concept for both series is the same, but the bolt hole spacing and flange head dimensions are larger for Code 62.

The female port is an threaded hole with four bolt holes in a rectangular pattern. The male consists of a flange head grooved for an o-ring, and either a captive flange or split flange halves with bolt holes to match the port. The seal occurs when the o-ring is compressed between the flange head and the flat surface surrounding the female port.

Flange
Bolt Flange
Flange Plug
Inch Size
Dash Size
61 Flange Head Diameter
62 Flange Head Diameter
1/2
08
1.19
1.25
3/4
12
1.50
1.63
1
16
1.75
1.88
1-1/4
20
2.00
2.13
1-1/2
24
2.38
2.50
2
32
2.81
3.13

Caterpillar Flange connections share the same specifications and dimensions as Code 62 flanges, but with a flange head thickness of .56".

Cat Flange Drawing
Bolt Flange
Cat Flange
Inch Size
Dash Size
Flange Head Thickness
Flange Head Diameter
1/2
08
.56
1.25
3/4
12
.56
1.63
1
16
.56
1.88
1-1/4
20
.56
2.13
1-1/2
24
.56
2.50
2
32
.56
3.13

SAE J512 45° connections are commonly used in refrigeration, automotive, and truck systems. The connectors is frequently made of brass, but still available in steel. Both male and female connectors have 45° seats. The seal takes place between the male flare and female cone. The threads hold the connection mechanically.Note – in sizes 02, 03, 04, 05, 08, and 10, the threads of SAE 37° and SAE 45° are the same, but the sealing surface angles are not.

 Flare Drawing
 Flare Cap
 45 Flare Plug
Inch Size
Dash Size
Thread Size
Male OD
Female ID
1/8
02
5/16-24
.31
.27
3/16
03
3/8-24
.38
.34
1/4
04
7/16-20
.44
.39
5/16
05
1/2-20
.50
.45
3/8
06
5/8-18
.63
.57
1/2
08
3/4-16
.75
.69
5/8
10
7/8-14
.88
.81
3/4
12
1-1/16 - 14
1.06
.99
7/8
14
1-1/4 - 12
1.25
1.16
1
16
1-3/8 - 12
1.38
1.29
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

SAE J512 Inverted Flare connections are frequently used in automotive systems. The male connector can either be a 45° flare in the tube fitting form, or a 42° seat in the machined adapter form. The female has a straight thread with a 42° inverted flare. The seal takes place on the flared surfaces. The threads hold the connection mechanically.

Inverted Flare Drawing
Inverted Tube Drawing
Inverted Flare
Inch Size
Dash Size
Thread Size
Male OD
Female ID
1/8
02
5/16-28
.32
.28
3/16
03
3/8-24
.38
.34
1/4
04
7/16-24
.44
.40
5/16
05
1/2-20
.50
.45
3/8
06
5/8-18
.63
.57
7/16
07
11/16-18
.69
.63
1/2
08
3/4-18
.75
.70
5/8
10
7/8-18
.88
.82
3/4
12
1-1/16 - 16
1.06
1.00
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

British Standard Pipe Tapered (BSPT) connections are similar to National Pipe threads, except that the thread pitches are different in most sizes, and the thread form and outside diameters are close but not exactly the same. Because of the similarities to National Pipe, it is recommenced to very thread pitch and diameter closely with BSPT connectors. Sealing is accomplished by thread deformation.

BSPT
BSPT Cap
BSPT Plug
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/8
02
1/8-28
.38
.35
1/4
04
1/4-19
.52
.47
3/8
06
3/8-19
.65
.60
1/2
08
1/2-14
.82
.75
5/8
10
5/8-14
.88
.80
3/4
12
3/4-14
1.04
.97
1
16
1-11
1.30
1.22
1-1/4
20
1-1/4 - 11
1.65
1.56
1-1/2
24
1-1/2 - 11
1.88
1.79
2
32
2-11
2.35
2.26
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread (subtract 1/4) and followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

British Standard Parallel (BSPP) connections are similar to National Pipe threads, except that the thread pitches are different in most sizes. The female swivel BSPP connector has a tapered nose/globeseal flareless swivel which seals on the cone seat of the male.

BSPP O-ring connections are also available in a "port" style which forgoes the chamfer in favor of a bonded seal which rests on the shoulder of the male and seals when compressed against the female. Some styles are available in "dual purpose" as well.

BSPP CONE
Cone Seat
BSPP Port
BSPP Port
Dual Purpose
Dual Purpose
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/8
02
1/8-28
.38
.35
1/4
04
1/4-19
.52
.47
3/8
06
3/8-19
.65
.60
1/2
08
1/2-14
.82
.75
5/8
10
5/8-14
.88
.80
3/4
12
3/4-14
1.04
.97
1
16
1-11
1.30
1.22
1-1/4
20
1-1/4 - 11
1.65
1.56
1-1/2
24
1-1/2 - 11
1.88
1.79
2
32
2-11
2.35
2.26
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

Japanese Industrial Standard, or JIS 30° Flare connections are similar to BSPP connections, and the threads of both fittings are interchangeable. JIS 30° fittings possess a cone that resembles JIC 37°, but have different flare angles and sealing principles.

While less commonly seen, JIS connectors are also available with a male inverted seat with metric threads, tapered pipe, and inverted male seat with parallel pipe threads. To identify these uncommon threads, please consult our downloadable guide or contact us for further assistance.

JIS Drawing
JIS Cap
JIS Plug
Inch Size
Dash Size
Nominal Size
Male OD
Female ID
1/4
4
1/4-19
.52
.47
3/8
6
3/8-19
.65
.60
1/2
8
1/2-14
.82
.75
3/4
12
3/4-14
1.04
.97
1
16
1-11
1.30
1.22
1-1/4
20
1-1/4-11
1.65
1.56
1-1/2
24
1-1/2-11
1.88
1.79
2
32
2-11
2.35
2.26
Inch Size - With adapter fittings, inch and dash size refer to the theoretical outside/inside diameter of the mating tube or hose expressed as either a fraction or 1/16 of an inch.

Nominal Size - Refers to the outside diameter of the male thread, followed by the number of threads per inch or TPI.

Male OD - Male OD and Female ID refer to the outside or inside diameter of a thread, expressed as either a fraction or decimal.

German DIN 7631 Series connections are often used in hydraulic systems. The male has a straight metric thread and a 60° recessed cone. The female has a straight thread and a tapered seat. The seal takes place by contact between the male cone and female nose/seat. The threads hold the connection mechanically.

DIN Drawing
DIN Cap
DIN PLug
Tube OD (mm)
Metric Thread Size
Male OD (mm)
Female ID (mm)
6
M12 X 1.5
12
10.5
8
M14 X 1.5
14
12.5
10
M16 X 1.5
16
14.5
12
M18 X 1.5
18
16.5
15
M22 X 1.5
22
20.5
18
M26 X 1.5
26
24.5
22
M30 X 1.5
30
28.5
28
M38 X 1.5
38
36.5
35
M45 X 1.5
45
43.5
42
M52 X 1.5
52
50.5

German DIN 3902 Series connections consist of a common male and three different female types. DIN 3902 threads are also available in extra light (LL), light (L), and heavy duty (S) series. Selection of proper series is paramount to ensuring accurate identification.

The male has a straight metric thread, a 24° included angle, and a recessed counter bore that matches the tube OD used with it. The female may be a tube, nut and ferrule, a tapered flareless swivel, or a flareless swivel with o-ring, referred to as DKO type.

DIN Drawings
DKO End
DIN Tube
Tube OD Light Series (mm)
Tube OD Heavy Series (mm)
Female Metric Thread Size
Thread OD (mm)
Thread ID (mm)
6
-
M12 X 1.5
12
10.5
8
6
M14 X 1.5
14
12.5
10
8
M16 X 1.5
16
14.5
12
10
M18 X 1.5
18
16.5
-
12
M20 X 1.5
20
18.5
15
14
M22 X 1.5
22
20.5
-
16
M24 X 1.5
24
22.5
18
-
M26 X 1.5
26
24.5
22
20
M30 X 2.0
30
28
28
25
M36 X 2.0
36
34
-
30
M42 X 2.0
42
40
35
-
M45 X 2.0
45
43
42
38
M52 X 2.0
52
50