A letter n drill measures 0.3020 inch (7.671 mm). The closest fractional drill is 19/64" (0.2969") and the closest metric drill is 7.7 mm (0.3031").
What are the letter n drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| N | letter | 0.3020 | 7.671 | 0 |
| 7.6 mm | metric | 0.2992 | 7.600 | -0.0028 |
| 7.7 mm | metric | 0.3031 | 7.700 | +0.0011 |
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 letter n drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 2,530 | 0.0060 |
| 360 free-machining brass | 1,897 | 0.0054 |
| 1018 cold rolled steel | 1,012 | 0.0045 |
| 304 stainless steel | 506 | 0.0030 |
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 letter n drill in inches?
0.3020 inch, which is 7.671 mm. Letter drills run from A (0.234 inch) to Z (0.413 inch), continuing upward from the number drills. If you do not have this exact size, 7.7 mm is within 0.0011 inch.
What tap uses a letter n 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.