1-8 UNC thread: 25.4 mm × 8 TPI

Threads › 1-8 UNC

1-8 UNC is a UNC thread: 25.4 mm major diameter, 8 TPI (3.175 mm pitch), 60° form. Tap drill 22.25 mm.

Minor diameters worked out from the basic profile: major Ø − 1.22687 × pitch (bolt) and − 1.08253 × pitch (nut).

Open 1-8 UNC 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

• 1-12 UNF12 TPI (2.117 mm pitch)
• 1 BSW8 TPI (3.175 mm pitch)

Close in size, won't mate

• 1-5 ACMEØ25.4 mm, 5 TPI
• Tr26×5Ø26 mm, 5 mm pitch

One size up or down

• 7/8-9 UNCØ22.23 mm (down)
• 1-1/8-7 UNCØ28.58 mm (up)

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