Letter N drill size
A letter N drill is 0.3020 in (7.67 mm). It sits between letter M and letter O in the letter series; the nearest metric drill is 7.7 mm.
Letter N 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 |
|---|---|---|---|---|
| 7.6 mm | 0.2992" | −0.071 mm | −0.0028" | Smaller |
| 7.7 mm | 0.3031" | +0.029 mm | +0.0011" | 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 | −0.0740" |
| Letter M | Letter | 0.2950" | 7.49 mm | −0.0070" |
| 19/64" | Fractional | 0.2969" | 7.54 mm | −0.0051" |
| Letter N | Letter | 0.3020" | 7.67 mm | this size |
| 5/16" | Fractional | 0.3125" | 7.94 mm | +0.0105" |
| Letter O | Letter | 0.3160" | 8.03 mm | +0.0140" |
Threads a Letter N 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 N 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" | 0.0520" | 0.0260" | – |
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 N drill?
A letter N drill is 0.3020 in, which is 7.67 mm (7.6708 mm exactly).
What is the metric equivalent of a letter N drill?
The nearest metric drill is 7.7 mm, 0.029 mm larger. The other close size is 7.6 mm.
Which fractional drill is closest to letter N?
19/64 in (0.2969 in) is the closest, 0.0051 in smaller.
What does a letter N drill clear?
It clears a 1/4" bolt with 0.0520" total clearance (0.0260" per side).