3/8 BSW thread: 9.52 mm × 16 TPI

Threads › 3/8 BSW

3/8 BSW is a BSW Whitworth thread: 9.52 mm major diameter, 16 TPI (1.588 mm pitch), 55° form. Tap drill 7.9 mm.

Minor diameters worked out from the basic profile: major Ø − 1.28065 × pitch.

Open 3/8 BSW in BenchsmithAdd to order list

Measure it

Bolt: Measure across the crests of the bolt with the caliper jaws. Worn bolts read 0.1 to 0.3 under.

Nut or tapped hole: Measure across the tops of the threads inside the nut or hole with the inside jaws. That is the minor Ø. Worn or oversize holes read a little over.

Same diameter, other pitch

• 3/8-16 UNC16 TPI (1.588 mm pitch)
• 3/8-24 UNF24 TPI (1.058 mm pitch)

Close in size, won't mate

• 3/8-12 ACMEØ9.52 mm, 12 TPI
• G1/8Ø9.73 mm, 28 TPI
• R1/8Ø9.73 mm, 28 TPI
• M10Ø10 mm, 1.5 mm pitch
• M10×1.25Ø10 mm, 1.25 mm pitch
• M10×1Ø10 mm, 1 mm pitch

One size up or down

• 5/16 BSWØ7.94 mm (down)
• 7/16 BSWØ11.11 mm (up)

Got a bolt and no idea what it is? Measure the outside Ø and type it into Benchsmith → Find → Thread.