A #4 drill measures 0.2090 inch (5.309 mm). The closest fractional drill is 13/64" (0.2031") and the closest metric drill is 5.3 mm (0.2087").
What are the #4 drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| #4 | number | 0.2090 | 5.309 | 0 |
| 5.3 mm | metric | 0.2087 | 5.300 | -0.0003 |
Drill sets that include this size
Number and letter sizes come in indexed sets; buy the set rather than single drills.
What speed should a #4 drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 3,655 | 0.0042 |
| 360 free-machining brass | 2,741 | 0.0038 |
| 1018 cold rolled steel | 1,462 | 0.0031 |
| 304 stainless steel | 731 | 0.0021 |
Starting points from conservative HSS drilling speeds. Small drills often call for more RPM than a benchtop drill press offers; run at the top speed and feed gently. Use cutting oil in steel and stainless, and clamp the work: never hold it by hand.
Cutting fluid for drilling
Frequently asked questions
What is a #4 drill in inches?
0.2090 inch, which is 5.309 mm. Number drills get smaller as the number rises, so the next number up is a smaller drill. If you do not have this exact size, 5.3 mm is within 0.0003 inch.
What tap uses a #4 drill?
No common UNC or UNF thread uses it as its standard 75% tap drill, but it often serves as an alternative drill for a slightly different percentage of thread, or as a clearance or pilot size. The tap drill chart lists every standard pairing.