A #28 drill measures 0.1405 inch (3.569 mm). The closest fractional drill is 9/64" (0.1406") and the closest metric drill is 3.6 mm (0.1417").
What are the #28 drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| #28 | number | 0.1405 | 3.569 | 0 |
| 3.5 mm | metric | 0.1378 | 3.500 | -0.0027 |
| 9/64" | fraction | 0.1406 | 3.572 | +0.0001 |
| 3.6 mm | metric | 0.1417 | 3.600 | +0.0012 |
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 #28 drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 5,437 | 0.0028 |
| 360 free-machining brass | 4,078 | 0.0025 |
| 1018 cold rolled steel | 2,175 | 0.0021 |
| 304 stainless steel | 1,087 | 0.0014 |
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 #28 drill in inches?
0.1405 inch, which is 3.569 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, 3.6 mm is within 0.0012 inch.
What tap uses a #28 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.