UNF tap-drill chart
Find a Unified National Fine thread by its diameter and threads per inch. A different pitch can require a different hole, even at the same major diameter.
Select a drill diameter to centre that hole on the chart while keeping its thread as the pinned base.
UNF thread sizes
| Thread & major diameter | Tap drill Open on chart ↗ |
|---|---|
#3-56 UNFBasic major Ø 2.5146 mm | Ø 2.1 mm |
#4-48 UNFBasic major Ø 2.8448 mm | Ø 2.35 mm |
#5-44 UNFBasic major Ø 3.175 mm | Ø 2.65 mm |
#6-40 UNFBasic major Ø 3.5052 mm | Ø 2.9 mm |
#8-36 UNFBasic major Ø 4.1656 mm | Ø 3.5 mm |
#10-32 UNFBasic major Ø 4.826 mm | Ø 4.1 mm |
#12-28 UNFBasic major Ø 5.4864 mm | Ø 4.6 mm |
1/4-28 UNFBasic major Ø 6.35 mm | Ø 5.5 mm |
5/16-24 UNFBasic major Ø 7.9375 mm | Ø 6.9 mm |
3/8-24 UNFBasic major Ø 9.525 mm | Ø 8.5 mm |
7/16-20 UNFBasic major Ø 11.1125 mm | Ø 9.8 mm |
1/2-20 UNFBasic major Ø 12.7 mm | Ø 11.5 mm |
9/16-18 UNFBasic major Ø 14.2875 mm | Ø 12.8 mm |
5/8-18 UNFBasic major Ø 15.875 mm | Ø 14.5 mm |
3/4-16 UNFBasic major Ø 19.05 mm | Ø 17.5 mm |
7/8-14 UNFBasic major Ø 22.225 mm | Ø 20.5 mm |
1-12 UNFBasic major Ø 25.4 mm | Ø 23.5 mm |
1 1/8-12 UNFBasic major Ø 28.575 mm | Ø 26.5 mm |
1 1/4-12 UNFBasic major Ø 31.75 mm | Ø 29.5 mm |
1 1/2-12 UNFBasic major Ø 38.1 mm | Ø 36 mm |
Recommendations vary with material, engagement and tool. These values are transcribed from the Alpha / Sterling chart, not calculated by subtracting pitch. They are not intended for forming taps. A nearby catalogue drill is a dimensional comparison, not a substitute recommendation.
Read the whole designation
In a designation such as 1/4-20 UNC, the fraction identifies the basic major diameter in inches and the second number specifies threads per inch. The family is part of the designation: UNC and UNF threads with the same major diameter can have different pitches.
Equal basic diameters do not establish compatibility. Confirm the pitch, thread form, tolerances and mating standard. Omitted sizes or pitches are outside this selected table, not evidence that they do not exist.
Sources & scope
Data edition 1.0. Values come from the reference sources below. SizeAxis is a selected reference catalogue; it does not certify manufactured dimensions or thread compatibility.
Read the measurement definitions and full coverage