#3-48 UNC tap drill size
Tap #3-48 UNC with a #47 drill (0.0785 in, 1.99 mm), about 76% thread. Taps this fine break easily, so hand-tap with cutting oil and back off often.
| Drill | inch | mm | Thread % | Typical use |
|---|---|---|---|---|
| #48 | 0.0760 | 1.93 | 85.0% | General purpose |
| 5/64" | 0.0781 | 1.98 | 77.1% | General purpose |
| #47 (chart drill) | 0.0785 | 1.99 | 75.7% | General purpose |
| 2.0 mm (metric drill) | 0.0787 | 2.0 | 74.9% | General purpose |
| #46 | 0.0810 | 2.06 | 66.5% | Hard or tough material, deep or blind holes |
| #45 | 0.0820 | 2.08 | 62.8% | Hard or tough material, deep or blind holes |
| Thread | Tap drill | Tap drill (mm) | Clearance close / free |
|---|---|---|---|
| #1-64 UNC | #53 (0.0595 in) | 1.51 mm | #48 / #46 |
| #2-56 UNC | #50 (0.0700 in) | 1.78 mm | #43 / #41 |
| #3-48 UNC (this page) | #47 (0.0785 in) | 1.99 mm | #37 / #35 |
| #4-40 UNC | #43 (0.0890 in) | 2.26 mm | #32 / #30 |
| #5-40 UNC | #38 (0.1015 in) | 2.58 mm | #30 / #29 |
Practical notes
At 48 TPI the basic thread depth is only about 0.0113 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 #3 sizes in aluminium and brass because they make no chips; they need a larger hole, roughly 0.0886 in (2.25 mm, D − 0.5 × pitch). Confirm against the tap maker's chart.
If a #3 thread in plastic or a printed part must survive repeated assembly, a threaded insert is usually more durable than tapping the base material.
UNC (coarse) is the default Unified series: quicker to assemble, more tolerant of dirt and damage, and better in soft materials such as aluminium and cast iron.
Clearance drills for a #3 screw: close fit #37 (0.1040 in, 2.64 mm), free fit #35 (0.1100 in, 2.79 mm).
FAQ
What size drill for a #3-48 UNC tap?
The standard tap drill for #3-48 UNC is a #47 drill, 0.0785 in (1.99 mm), which gives about 76% thread.
What clearance hole for a #3 UNC screw?
Use #37 (0.1040 in, 2.64 mm) for a close fit or #35 (0.1100 in, 2.79 mm) for a free fit. Clearance depends on diameter only, so it is the same for UNC and UNF #3 screws.
What metric drill can I use for #3-48 UNC?
The closest metric drill is 2.0 mm (0.0787 in), giving about 75% thread on #3-48 UNC.
What is the difference between #3-48 UNC and #3-56 UNF?
Both are #3 diameter. #3-48 UNC has 48 threads per inch and uses a #47 tap drill (0.0785 in); #3-56 UNF has 56 TPI and uses a #45 drill (0.0820 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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