Unified inch · UNF

#5-44 UNF tap drill size

For general work, OSG suggests 65–70% of full thread. Harder materials and deep holes want less; the calculator sets it from your material.

Cut tap

#37

0.1040" · 71% thread

Form tap

#32

0.1160" · 58% thread

Or 2.9 mm for 70%

Open #5-44 UNF in the calculator

Pick your material for its % of thread, tapping RPM and the rigid-tap code.

Thread dimensions

Major Ø: 0.1250" (3.175 mm)
Threads per inch: 44 (pitch 0.0227")
Pitch Ø (basic): 0.1102" (2.800 mm)
Minor Ø (internal, basic): 0.1004" (2.550 mm)
Thread depth (internal): 0.0123" (0.312 mm)

Basic sizes of the 60° form. Tolerance classes (2B/3B) set the limits around them.

Cut tap drills

For a cutting (fluted or spiral) tap. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Cut tap drills for #5-44 UNF
Drill	Ø in	Ø mm	Thread
#38	0.1015	2.58	80%
2.6 mm	0.1024	2.60	77%
#37	0.1040	2.64	71%
2.7 mm	0.1063	2.70	63%
#36	0.1065	2.71	63%
7/64	0.1094	2.78	53%
#35	0.1100	2.79	51%
2.8 mm	0.1102	2.80	50%

Form tap drills

A form (roll) tap displaces metal instead of cutting it, so it needs a bigger hole. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Form tap drills for #5-44 UNF
Drill	Ø in	Ø mm	Thread
#33	0.1130	2.87	78%
2.9 mmsuggested	0.1142	2.90	70%
#32	0.1160	2.95	58%

3-wire measurement

Best wire size: 0.0131" (0.333 mm)
Over wires, at basic pitch Ø: 0.1299" (3.300 mm)

For the external thread (the screw). The best wire touches the flanks at the pitch diameter.

Sources

ASME B1.1 — Unified Inch Screw Threads (UN and UNR thread form)
OSG — Tap drill size and pitch diameter limit chart (formula, suggested % of full thread)
Cutting Tool Engineering — "Threads will roll": form tap hole size = D − 0.0068 × % / TPI
ASME B94.11M — Twist drills (fractional, number, letter and metric sizes)
NIST (NBS) Letter Circular 23 and Pratt & Whitney — three-wire thread measurement, best wire size