Letter P drill size
A letter P drill is 0.3230 in (8.20 mm). It sits between letter O and letter Q in the letter series; the nearest metric drill is 8.2 mm.
Letter P 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 |
|---|---|---|---|---|
| 8.2 mm | 0.3228" | −0.004 mm | −0.0002" | Smaller |
| 8.3 mm | 0.3268" | +0.096 mm | +0.0038" | 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 | −0.0950" |
| 5/16" | Fractional | 0.3125" | 7.94 mm | −0.0105" |
| Letter O | Letter | 0.3160" | 8.03 mm | −0.0070" |
| Letter P | Letter | 0.3230" | 8.20 mm | this size |
| 21/64" | Fractional | 0.3281" | 8.33 mm | +0.0051" |
| Letter Q | Letter | 0.3320" | 8.43 mm | +0.0090" |
Threads a Letter P drill can tap
Threads from the tap tables on this site that this drill can tap, with the thread percentage it leaves (55–85 % shown).
| Thread | Standard drill | Thread with this drill | Suits |
|---|---|---|---|
| 3/8-16 UNC | 5/16 | 64 % | Hard, tough metals |
Clearance for screws and bolts
Bolts and screws a Letter P 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 |
|---|---|---|---|---|
| 5/16" bolt | 0.3125" | 0.0105" | 0.0053" | – |
| M8 bolt | 8 mm | 0.20 mm | 0.10 mm | Tighter than close fit (8.4 mm) |
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 P drill?
A letter P drill is 0.3230 in, which is 8.20 mm (8.2042 mm exactly).
What is the metric equivalent of a letter P drill?
The nearest metric drill is 8.2 mm, 0.004 mm smaller. The other close size is 8.3 mm.
What thread can I tap with a letter P drill?
It leaves about 64 % thread in 3/8-16 UNC.
Which fractional drill is closest to letter P?
21/64 in (0.3281 in) is the closest, 0.0051 in larger.
What does a letter P drill clear?
It clears a M8 bolt with 0.20 mm total clearance (0.10 mm per side); for metric bolts: tighter than close fit.