1/2 BSW thread: 12.7 mm × 12 TPI

Threads › 1/2 BSW

1/2 BSW is a BSW Whitworth thread: 12.7 mm major diameter, 12 TPI (2.117 mm pitch), 55° form. Tap drill 10.5 mm.

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

Open 1/2 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

• 1/2-13 UNC13 TPI (1.954 mm pitch)
• 1/2-20 UNF20 TPI (1.27 mm pitch)

Close in size, won't mate

• 1/2-10 ACMEØ12.7 mm, 10 TPI
• G1/4Ø13.16 mm, 19 TPI
• R1/4Ø13.16 mm, 19 TPI
• M12Ø12 mm, 1.75 mm pitch
• M12×1.5Ø12 mm, 1.5 mm pitch
• M12×1.25Ø12 mm, 1.25 mm pitch

One size up or down

• 7/16 BSWØ11.11 mm (down)
• 9/16 BSWØ14.29 mm (up)

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