UNC tap-drill chart
Find a Unified National Coarse thread by its diameter and threads per inch. Each drill value is the source’s cutting-tap recommendation.
Select a drill diameter to centre that hole on the chart while keeping its thread as the pinned base.
UNC thread sizes
| Thread & major diameter | Tap drill Open on chart ↗ |
|---|---|
#2-56 UNCBasic major Ø 2.1844 mm | Ø 1.85 mm |
#3-48 UNCBasic major Ø 2.5146 mm | Ø 2.1 mm |
#4-40 UNCBasic major Ø 2.8448 mm | Ø 2.3 mm |
#5-40 UNCBasic major Ø 3.175 mm | Ø 2.6 mm |
#6-32 UNCBasic major Ø 3.5052 mm | Ø 2.8 mm |
#8-32 UNCBasic major Ø 4.1656 mm | Ø 3.4 mm |
#10-24 UNCBasic major Ø 4.826 mm | Ø 3.8 mm |
#12-24 UNCBasic major Ø 5.4864 mm | Ø 4.5 mm |
1/4-20 UNCBasic major Ø 6.35 mm | Ø 5.1 mm |
5/16-18 UNCBasic major Ø 7.9375 mm | Ø 6.6 mm |
3/8-16 UNCBasic major Ø 9.525 mm | Ø 8 mm |
7/16-14 UNCBasic major Ø 11.1125 mm | Ø 9.4 mm |
1/2-13 UNCBasic major Ø 12.7 mm | Ø 10.8 mm |
9/16-12 UNCBasic major Ø 14.2875 mm | Ø 12.2 mm |
5/8-11 UNCBasic major Ø 15.875 mm | Ø 13.5 mm |
3/4-10 UNCBasic major Ø 19.05 mm | Ø 16.5 mm |
7/8-9 UNCBasic major Ø 22.225 mm | Ø 19.5 mm |
1-8 UNCBasic major Ø 25.4 mm | Ø 22.2 mm |
1 1/8-7 UNCBasic major Ø 28.575 mm | Ø 25 mm |
1 1/4-7 UNCBasic major Ø 31.75 mm | Ø 28 mm |
1 3/8-6 UNCBasic major Ø 34.925 mm | Ø 31 mm |
1 1/2-6 UNCBasic major Ø 38.1 mm | Ø 34 mm |
1 3/4-5 UNCBasic major Ø 44.45 mm | Ø 39.5 mm |
2-4.5 UNCBasic major Ø 50.8 mm | Ø 45 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