Tap Drill Size Chart

UNF Tap Drill Chart

Tap drill sizes for every UNF (Unified National Fine) thread, from #0-80 to 1-1/2-12. Fine threads have more threads per inch than the coarse UNC versions at the same diameter, so they are shallower and take a larger tap drill. Sort any column, filter by size, and click a row for that size's full page.

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24 sizes

UNF tap drill sizes: size, tap drill, decimal inch, millimetres, percent of thread, hard-material drill, form-tap drill, basic minor diameter and threads per inch.
#0-80 3/64″ 0.0469 1.19 80.7
#1-72 #53 0.0595 1.51 74.8
#2-64 #50 0.070 1.78 78.8
#3-56 #45 0.082 2.08 73.3
#4-48 #42 0.0935 2.38 68.4
#5-44 #37 0.104 2.64 71.1
#6-40 #33 0.113 2.87 77.0
#8-36 #29 0.136 3.45 77.6
#10-32 #21 0.159 4.04 76.4
#12-28 #14 0.182 4.62 73.3
1/4-28 #3 0.213 5.41 79.8
5/16-24 I 0.272 6.91 74.8
3/8-24 Q 0.332 8.43 79.4
7/16-20 25/64″ 0.3906 9.92 72.2
1/2-20 29/64″ 0.4531 11.51 72.2
9/16-18 33/64″ 0.5156 13.10 65.0
5/8-18 37/64″ 0.5781 14.68 65.0
3/4-16 11/16″ 0.6875 17.46 77.0
7/8-14 13/16″ 0.8125 20.64 67.4
1-12 59/64″ 0.9219 23.42 72.1
1-1/8-12 1-3/64″ 1.0469 26.59 72.1
1-1/4-12 1-11/64″ 1.1719 29.77 72.1
1-3/8-12 1-19/64″ 1.2969 32.94 72.1
1-1/2-12 1-27/64″ 1.4219 36.12 72.1

Tap a column heading to sort. Every row links to that size's full page.

When a fine thread is the right choice

Fine threads earn their keep in four places: thin walls, where a coarse thread would not get enough turns into the material; short engagement, for the same reason; fine adjustment, because each turn moves the fastener less; and hard material, where the shallower thread is easier on the tap.

They are the wrong choice in soft or brittle material, in anything that gets dirty or corroded, and in joints taken apart often. A fine thread cross-threads more easily and its shallower engagement strips sooner in aluminium or plastic. For that work, use the coarse UNC sizes.

Fine threads need the hole size right

There is less room for error here than on a coarse thread. The whole thread is shallower, so the same amount of drill oversize eats a bigger share of it. Going one drill size too large on a fine thread costs more percent of thread than the same step would on the coarse version of that diameter.

That cuts both ways. Going one size too small raises tapping torque sharply, and fine taps are the ones that snap. If you are tapping stainless or tool steel, use the hard-material column rather than the standard drill.

The same diameter in both series

Every size on this chart has a coarse counterpart on the UNC chart, and some have an extra-fine one on the UNEF chart. They share a major diameter and nothing else: different pitch, different tap, different drill, and fasteners that will not swap. Each size's own page lists its siblings so you can check before you cut.

Frequently asked questions

What is a UNF thread?
UNF stands for Unified National Fine. Same diameters as UNC, more threads per inch. A 1/4-28 is UNF; a 1/4-20 is UNC. This chart lists all 24 UNF sizes with their tap drills.
What drill do I use for a 10-32 tap?
A #21 drill, 0.159 in, which leaves 76.4% of thread. 10-32 is the most looked-up fine thread.
Is a fine thread stronger than a coarse one?
In tension, slightly. A fine thread has a larger tensile stress area because its minor diameter is bigger, so there is more metal in the bolt. That advantage disappears in soft material, where the internal thread strips before the bolt breaks, and coarse threads hold better there.
Why is the fine tap drill bigger than the coarse one at the same diameter?
Because a fine thread is shallower. 1/4-20 takes #7 (0.201 in) and 1/4-28 takes #3 (0.213 in). Less thread height means less material to remove, so the hole starts closer to the major diameter.
Can I run a fine tap into a hole drilled for a coarse one?
You can, but the hole will be too small and the thread far deeper than it should be, which means much more torque and a real chance of snapping the tap. Drill the right size or open the hole up first.

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