A #23 drill measures 0.1540 inch (3.912 mm). The closest fractional drill is 5/32" (0.1563") and the closest metric drill is 3.9 mm (0.1535").
What are the #23 drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| #23 | number | 0.1540 | 3.912 | 0 |
| #24 | number | 0.1520 | 3.861 | -0.0020 |
| 3.9 mm | metric | 0.1535 | 3.900 | -0.0005 |
| 5/32" | fraction | 0.1563 | 3.969 | +0.0023 |
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 #23 drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 4,961 | 0.0031 |
| 360 free-machining brass | 3,721 | 0.0028 |
| 1018 cold rolled steel | 1,984 | 0.0023 |
| 304 stainless steel | 992 | 0.0015 |
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 #23 drill in inches?
0.1540 inch, which is 3.912 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, 3.9 mm is within 0.0005 inch.
What tap uses a #23 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.