UNF — Unified fine

#1-72 UNF

Tap drill #53 for a #1-72 UNF thread — major Ø 1.854 mm, pitch 0.353 mm (72 TPI).

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Tap drill

#53

1.51 mm · ≈75% thread

Profile

Thread form & key diameters

Dimensions

Designation	#1-72 UNF
Major (outside) diameter	1.854 mm · 0.073"
Pitch	0.353 mm · 72 TPI
Pitch diameter	1.625 mm · 0.064"
Minor diameter (external)	1.421 mm · 0.056"
Minor diameter (internal)	1.472 mm · 0.058"
Recommended tap drill	#53 · 1.51 mm · ≈75% thread
Clearance hole	Close #43 · Normal #37 · Loose #29 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Socket key (across flats)	1/16"

Close #43 · Normal #37 · Loose #29 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).

What tap drill do I need for #1-72 UNF?

For a #1-72 UNF thread, drill the hole with a #53 tap drill (1.51 mm) before tapping. That produces roughly 75% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 1.854 mm and a pitch of 0.353 mm (72 TPI).

To pass a #1-72 UNF bolt through a part rather than thread it, use a clearance hole: Close #43 · Normal #37 · Loose #29 — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice)..

All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables — not hand-entered. See the full reference.

Same diameter

Other #1 threads

#1-64 UNCTap #53Ø 1.854 mm · pitch 0.397 mm

Nearby sizes

More unf — unified fine threads

#0-80 UNFTap 3/64"Ø 1.524 mm · pitch 0.318 mm #2-64 UNFTap #50Ø 2.184 mm · pitch 0.397 mm #3-56 UNFTap #45Ø 2.515 mm · pitch 0.454 mm #4-48 UNFTap #42Ø 2.845 mm · pitch 0.529 mm #5-44 UNFTap #37Ø 3.175 mm · pitch 0.577 mm #6-40 UNFTap #33Ø 3.505 mm · pitch 0.635 mm #8-36 UNFTap #29Ø 4.166 mm · pitch 0.706 mm #10-32 UNFTap #21Ø 4.826 mm · pitch 0.794 mm