A #3 drill measures 0.2130 inch (5.410 mm). The closest fractional drill is 7/32" (0.2188") and the closest metric drill is 5.4 mm (0.2126"). It is the standard tap drill for 1/4-28.
What are the #3 drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| #3 | number | 0.2130 | 5.410 | 0 |
| 5.4 mm | metric | 0.2126 | 5.400 | -0.0004 |
Tap drill for: 1/4-28.
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 #3 drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 3,587 | 0.0043 |
| 360 free-machining brass | 2,690 | 0.0038 |
| 1018 cold rolled steel | 1,435 | 0.0032 |
| 304 stainless steel | 717 | 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 #3 drill in inches?
0.2130 inch, which is 5.410 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, 5.4 mm is within 0.0004 inch.
What tap uses a #3 drill?
It is the standard 75% thread tap drill for 1/4-28. Tap drills are chosen to leave about 75% of full thread depth, the balance of strength and tapping torque that published charts use.