25/64" drill size
A 25/64 in drill is 0.3906 in (9.92 mm). It is the standard tap drill for 7/16-20 UNF; the nearest metric drill is 9.9 mm.
25/64" at a glance
Decimal, metric and the nearest sizes in the other series.
- Decimal inch
- 0.3906"
- Millimetres
- 9.92 mm 9.9219
- Nearest metric drill
- 9.9 mm −0.022 mm
- Nearest letter drill
- Letter W 0.3860", −0.0046"
- Hole area
- 0.120 in² 77.3 mm²
- Tap drill for
- 7/16-20 UNF
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 |
|---|---|---|---|---|
| 9.9 mm | 0.3898" | −0.022 mm | −0.0009" | Smaller |
| 10.0 mm | 0.3937" | +0.078 mm | +0.0031" | 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 | −0.1626" |
| 3/8" | Fractional | 0.3750" | 9.52 mm | −0.0156" |
| Letter W | Letter | 0.3860" | 9.80 mm | −0.0046" |
| 25/64" | Fractional | 0.3906" | 9.92 mm | this size |
| Letter X | Letter | 0.3970" | 10.08 mm | +0.0064" |
| 13/32" | Fractional | 0.4062" | 10.32 mm | +0.0156" |
Threads a 25/64" 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 |
|---|---|---|---|
| 7/16-20 UNF | 25/64 | 72 % | Standard drill |
Clearance for screws and bolts
Bolts and screws a 25/64" 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 |
|---|---|---|---|---|
| M8 bolt | 8 mm | 1.92 mm | 0.96 mm | Normal fit (normal 9, loose 10 mm) |
| 3/8" bolt | 0.3750" | 0.0156" | 0.0078" | – |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Fractional drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a 25/64 in drill?
A 25/64 in drill is 0.3906 in, which is 9.92 mm (9.9219 mm exactly).
What is the metric equivalent of a 25/64 in drill?
The nearest metric drill is 9.9 mm, 0.022 mm smaller. The other close size is 10.0 mm.
What tap uses a 25/64 in drill?
A 25/64 in drill is the standard tap drill for 7/16-20 UNF (about 72 % thread).
Which number or letter drill is closest to 25/64 in?
Letter W (0.3860 in) is the closest, 0.0046 in smaller.
What does a 25/64 in drill clear?
It clears a 3/8" bolt with 0.0156" total clearance (0.0078" per side).