5/16 BSW thread: 7.94 mm × 18 TPI

Threads › 5/16 BSW

5/16 BSW is a BSW Whitworth thread: 7.94 mm major diameter, 18 TPI (1.411 mm pitch), 55° form. Tap drill 6.5 mm.

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

Open 5/16 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

• 5/16-18 UNC18 TPI (1.411 mm pitch)
• 5/16-24 UNF24 TPI (1.058 mm pitch)

Close in size, won't mate

• 5/16-14 ACMEØ7.94 mm, 14 TPI
• M8Ø8 mm, 1.25 mm pitch
• M8×1Ø8 mm, 1 mm pitch
• Tr8×1.5Ø8 mm, 1.5 mm pitch
• G1/16Ø7.72 mm, 28 TPI

One size up or down

• 1/4 BSWØ6.35 mm (down)
• 3/8 BSWØ9.52 mm (up)

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