5/16" drill size
A 5/16 in drill is 0.3125 in (7.94 mm). It is the standard tap drill for 3/8-16 UNC; the nearest metric drill is 7.9 mm.
5/16" at a glance
Decimal, metric and the nearest sizes in the other series.
- Decimal inch
- 0.3125"
- Millimetres
- 7.94 mm 7.9375
- Nearest metric drill
- 7.9 mm −0.037 mm
- Nearest letter drill
- Letter O 0.3160", +0.0035"
- Hole area
- 0.0767 in² 49.48 mm²
- Tap drill for
- 3/8-16 UNC
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 |
|---|---|---|---|---|
| 7.9 mm | 0.3110" | −0.037 mm | −0.0015" | Smaller |
| 8.0 mm | 0.3150" | +0.062 mm | +0.0025" | 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 | −0.0845" |
| 19/64" | Fractional | 0.2969" | 7.54 mm | −0.0156" |
| Letter N | Letter | 0.3020" | 7.67 mm | −0.0105" |
| 5/16" | Fractional | 0.3125" | 7.94 mm | this size |
| Letter O | Letter | 0.3160" | 8.03 mm | +0.0035" |
| 21/64" | Fractional | 0.3281" | 8.33 mm | +0.0156" |
Threads a 5/16" 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 | 77 % | Standard drill |
Clearance for screws and bolts
Bolts and screws a 5/16" 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" | 0.0625" | 0.0312" | – |
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 5/16 in drill?
A 5/16 in drill is 0.3125 in, which is 7.94 mm (7.9375 mm exactly).
What is the metric equivalent of a 5/16 in drill?
The nearest metric drill is 7.9 mm, 0.037 mm smaller. The other close size is 8.0 mm.
What tap uses a 5/16 in drill?
A 5/16 in drill is the standard tap drill for 3/8-16 UNC (about 77 % thread).
Which number or letter drill is closest to 5/16 in?
Letter O (0.3160 in) is the closest, 0.0035 in larger.
What does a 5/16 in drill clear?
It clears a 1/4" bolt with 0.0625" total clearance (0.0312" per side).