A letter m drill measures 0.2950 inch (7.493 mm). The closest fractional drill is 19/64" (0.2969") and the closest metric drill is 7.5 mm (0.2953").
What are the letter m drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| M | letter | 0.2950 | 7.493 | 0 |
| 7.5 mm | metric | 0.2953 | 7.500 | +0.0003 |
| 19/64" | fraction | 0.2969 | 7.541 | +0.0019 |
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 m drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 2,590 | 0.0059 |
| 360 free-machining brass | 1,942 | 0.0053 |
| 1018 cold rolled steel | 1,036 | 0.0044 |
| 304 stainless steel | 518 | 0.0029 |
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 m drill in inches?
0.2950 inch, which is 7.493 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, 7.5 mm is within 0.0003 inch.
What tap uses a letter m 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.