# 33/64" drill size

A 33/64 in drill is 0.5156 in (13.10 mm). It is the standard tap drill for 9/16-18 UNF; the nearest metric drill is 13.1 mm.

## 33/64" drill data

- Series: Fractional drill
- Decimal: 0.5156 in
- Metric: 13.10 mm (13.0969 mm exact)
- Nearest metric drill: 13.1 mm (+0.003 mm)
- Standard tap drill for: 9/16-18 UNF

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 13.0 mm | 0.5118 | −0.097 mm |
| 13.1 mm | 0.5157 | +0.003 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 1/2" | Fractional | 0.5000 | 12.70 |
| 33/64" | Fractional | 0.5156 | 13.10 |
| 17/32" | Fractional | 0.5312 | 13.49 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 9/16-18 UNF | 33/64 | 65 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M12 bolt | 12 mm | 1.10 mm | 0.55 mm | Close fit (close 13, normal 13.5 mm) |
| 1/2" bolt | 0.5000" | 0.0156" | 0.0078" | – |


## FAQ

**What size is a 33/64 in drill?**
A 33/64 in drill is 0.5156 in, which is 13.10 mm (13.0969 mm exactly).

**What is the metric equivalent of a 33/64 in drill?**
The nearest metric drill is 13.1 mm, 0.003 mm larger. The other close size is 13.0 mm.

**What tap uses a 33/64 in drill?**
A 33/64 in drill is the standard tap drill for 9/16-18 UNF (about 65 % thread).

**What does a 33/64 in drill clear?**
It clears a 1/2" bolt with 0.0156" total clearance (0.0078" per side).

Source page: https://machinistcharts.com/drill-size/33-64-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)