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Measuring Threads and Seat Angles

Measuring Threads

With the caliper, measure the thread diameter of the largest point. (Outside Diameter (O.D.) of male threads – Inside Diameter (I.D.) of female threads.)

Using the thread gauge, determine the number of threads per inch. Comparison of gauge and coupling threads against a lighted background will ensure an accurate reading.

Illustration of measuring the thread gauge

Match the measurements taken above against those in the following tables that appear similar to the coupling under consideration.

Measuring Seat Angles

Using the seat gauge, determine the angle of the seat, as illustrated. When the centerline of the seat gauge extends parallel with the projected longitudinal axis of the coupling, the angles of the gauge and seat match.

illustration show the right and wrong way to measure seat angles
illustration showing measuring seat angle of DIN 37 and 24

Compare the measurements taken to a coupling shown in the following tables that appear to be similar.

NOTE: Thread binding will occur when different thread configurations are used. DO NOT mix thread configurations.

Thread Chart

DASH SIZE2345678101214162024324048
NPTF Pipe
Thread		1/8–271/4–183/8–181/2–143/4–141–11-1/21-1/4–11-1/21-1/2–11-1/22–11-1/22-1/2–83–8
NPSM Swivel
Thread		1/8–271/4–183/8–181/2–143/4–141–11-1/21-1/4–11-1/21-1/2–11-1/22–11-1/2
JIC 37° Flare Thread5/16–243/8–247/16–201/2–209/16–183/4–167/8–141-1/16–121-3/16–121-5/16–121-5/8–121-7/8–122-1/2–123–123-1/2–12
SAE 45° Flare
Thread		5/16–243/8–247/16–201/2–205/8–1811/16–163/4–167/8–141-1/16–14
SAE O-Ring
Thread		5/16–243/8–247/16–201/2–209/16–183/4–167/8–141-1/16–121-3/16–121-5/16–121-5/8–121-7/8–122-1/2–12
Flat-Face Thread9/16–1811/16–1613/16–161–141-3/16–121-7/16–121-11/16–122–12
Inverted Flare
Thread		5/16–283/8–247/16–241/2–205/8–1811/16–183/4–187/8–181/16–16
Compression
Thread		5/16–243/8–247/16–241/2–249/16–245/8–2411/16–2013/16–181–18
Code 61 Flange
Head O.D.		1.191.341.501.752.002.382.813.314.00
Code 62 Flange Head O.D.1.251.621.882.122.503.12
BSPP Thread1/8–281/4–193/8–191/2–145/8–143/4–141–111-1/4–111-1/2–112–11
BSPT Thread1/8–281/4–193/8–191/2–145/8–143/4–141–111-1/4–111-1/2–112–11
Japanese Pipe Tapered Thread1/8–281/4–193/8–191/2–145/8–143/4–141–111-1/4–111-1/2–112–11
Japanese Flare
Thread		1/8–281/4–193/8–191/2–145/8–143/4–141–111-1/4–111-1/2–112–11
Copper/Nylon Air
Brake Thread		7/16–2417/32–2411/16–2013/16–181–18
METRIC (mm)8101214161820222426303336424552
Whitworth8X1.010X1.012X1.516X1.518X1.522X1.5
MDLM12X1.5M14X1.5M16X1.5M18X1.5M22X1.5M26X1.5M30X2.0M36X2.0M45X2.0M52X2.0
MDHM16X1.5M18X1.5M20X1.5M24X1.5M30X2.0M36X2.0M42X2.0M45X2.0M52X2.0
KomatsuM18X1.5M22X1.5M24X1.5M30X1.5M33X1.5M36X1.5M42X1.5
FrenchM20X1.5M24X1.5M30X1.5M36X1.5M45X1.5M52X1.5