#1-72 UNF tap drill size
Tap #1-72 UNF with a #53 drill (0.0595 in, 1.51 mm), about 75% thread. Taps this fine break easily, so hand-tap with cutting oil and back off often.
| Drill | inch | mm | Thread % | Typical use |
|---|---|---|---|---|
| 1.5 mm (metric drill) | 0.0591 | 1.5 | 77.3% | General purpose |
| #53 (chart drill) | 0.0595 | 1.51 | 74.8% | General purpose |
| 1/16" | 0.0625 | 1.59 | 58.2% | Low engagement: check strength |
| Thread | Tap drill | Tap drill (mm) | Clearance close / free |
|---|---|---|---|
| #0-80 UNF | 3/64" (0.0469 in) | 1.19 mm | #52 / #50 |
| #1-72 UNF (this page) | #53 (0.0595 in) | 1.51 mm | #48 / #46 |
| #2-64 UNF | #50 (0.0700 in) | 1.78 mm | #43 / #41 |
| #3-56 UNF | #45 (0.0820 in) | 2.08 mm | #37 / #35 |
| #4-48 UNF | #42 (0.0935 in) | 2.37 mm | #32 / #30 |
Practical notes
At 72 TPI the basic thread depth is only about 0.0075 in per side, so small errors in drill size change engagement a lot. Use a sharp, correctly sized drill, a tap guide to keep the tap square, and limit thread depth to about 1.5 × diameter.
Thread-forming taps are popular for #1 sizes in aluminium and brass because they make no chips; they need a larger hole, roughly 0.0661 in (1.68 mm, D − 0.5 × pitch). Confirm against the tap maker's chart.
If a #1 thread in plastic or a printed part must survive repeated assembly, a threaded insert is usually more durable than tapping the base material.
UNF (fine) threads have more threads per inch than UNC, a larger tensile stress area and better resistance to loosening, but they strip more easily in soft material and are more sensitive to drill size.
Clearance drills for a #1 screw: close fit #48 (0.0760 in, 1.93 mm), free fit #46 (0.0810 in, 2.06 mm).
FAQ
What size drill for a #1-72 UNF tap?
The standard tap drill for #1-72 UNF is a #53 drill, 0.0595 in (1.51 mm), which gives about 75% thread.
What clearance hole for a #1 UNF screw?
Use #48 (0.0760 in, 1.93 mm) for a close fit or #46 (0.0810 in, 2.06 mm) for a free fit. Clearance depends on diameter only, so it is the same for UNC and UNF #1 screws.
What metric drill can I use for #1-72 UNF?
The closest metric drill is 1.5 mm (0.0591 in), giving about 77% thread on #1-72 UNF.
What is the difference between #1-72 UNF and #1-64 UNC?
Both are #1 diameter. #1-72 UNF has 72 threads per inch and uses a #53 tap drill (0.0595 in); #1-64 UNC has 64 TPI and uses a #53 drill (0.0595 in). The threads are not interchangeable.
Sources: ASME B1.1 — Unified inch screw threads (UN and UNR form) · Machinery's Handbook — tap drill sizes and percentage-of-thread formula · ASME B94.11M — twist drills (number and letter drill sizes) · Common machinist clearance-drill chart (close / free fit)
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