Letter M drill size
A letter M drill is 0.2950 in (7.49 mm). It sits between letter L and letter N in the letter series; the nearest metric drill is 7.5 mm.
Letter M at a glance
Decimal, metric and the nearest sizes in the other series.
Nearest metric drills
Metric drills step by 0.05 mm below 3 mm and by 0.1 mm from 3 mm. Difference is metric minus inch size.
| Metric drill | Inch | Difference | In inches | Hole |
|---|---|---|---|---|
| 7.4 mm | 0.2913" | −0.093 mm | −0.0037" | Smaller |
| 7.5 mm | 0.2953" | +0.007 mm | +0.0003" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
| Drill | Series | Inch | mm | Difference |
|---|---|---|---|---|
| #1 | Number | 0.2280" | 5.79 mm | −0.0670" |
| 9/32" | Fractional | 0.2812" | 7.14 mm | −0.0137" |
| Letter L | Letter | 0.2900" | 7.37 mm | −0.0050" |
| Letter M | Letter | 0.2950" | 7.49 mm | this size |
| 19/64" | Fractional | 0.2969" | 7.54 mm | +0.0019" |
| Letter N | Letter | 0.3020" | 7.67 mm | +0.0070" |
Threads a Letter M drill can tap
No thread in the tap tables on this site falls between 55 and 85 % thread with this drill, so it is not a useful tap drill for them. Drills this size are mostly used for clearance, pilot and pin holes.
Clearance for screws and bolts
Bolts and screws a Letter M hole clears, with the diametral clearance and the gap each side. Metric sizes are compared with ISO 273.
| Fastener | Diameter | Clearance | Per side | ISO 273, metric only |
|---|---|---|---|---|
| 1/4" bolt | 0.2500" | 0.0450" | 0.0225" | – |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Letter drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a letter M drill?
A letter M drill is 0.2950 in, which is 7.49 mm (7.4930 mm exactly).
What is the metric equivalent of a letter M drill?
The nearest metric drill is 7.5 mm, 0.007 mm larger. The other close size is 7.4 mm.
Which fractional drill is closest to letter M?
19/64 in (0.2969 in) is the closest, 0.0019 in larger.
What does a letter M drill clear?
It clears a 1/4" bolt with 0.0450" total clearance (0.0225" per side).