What drill for a 2-1/4-4.5 roll (form) tap?

About 2.1518 in; the nearest standard drill is 2-5/32. Check your tap maker's table.

2-1/4-4.5 tap drill size

Use a 2-1/32 drill (2.0313 in) for a 2-1/4-4.5 cutting tap at 75% thread.

Drills for 2-1/4-4.5 (UNC)
Tap type	Drill	Decimal (in)
Cutting tap, 75% thread	2-1/32	2.0313
Cutting tap, 50% thread (hard material)	2-7/64	2.1094
Roll / form tap, 65% thread	2-5/32	2.1563

Pitch: 5.6444 mm (4.5 TPI)
Major Ø: 2.2500
Pitch Ø: 2.1057
Minor Ø: 2.0094

Open the tap drill calculator Roll tap chart Helicoil chart

Common questions

What size drill for a 2-1/4-4.5 tap?: Use a 2-1/32 drill (2.0313 in) for a 2-1/4-4.5 cutting tap at 75% thread.
What drill for a 2-1/4-4.5 roll (form) tap?: About 2.1518 in; the nearest standard drill is 2-5/32. Check your tap maker's table.

Other UNC sizes

Drill sizes from Machinery's Handbook and ASME B1.1/B1.13M; roll tap sizes from the form-tap formula. Tap and insert makers' tables are authoritative.

Free for machinists & programmers

Put your skills on a free talent profile

Machines, controls, certs and saved calculations in one profile shops can find.

Create free profile

For your shop

Bring shift handoffs to your shop

Stop losing job status between shifts. Every station's notes, counts and issues, handed off cleanly.

See shift handoffs