# 27/64" drill size

A 27/64 in drill is 0.4219 in (10.72 mm). It is the standard tap drill for 1/2-13 UNC; the nearest metric drill is 10.7 mm.

## 27/64" drill data

- Series: Fractional drill
- Decimal: 0.4219 in
- Metric: 10.72 mm (10.7156 mm exact)
- Nearest metric drill: 10.7 mm (−0.016 mm)
- Nearest letter drill: Letter Z (0.4130 in)
- Standard tap drill for: 1/2-13 UNC

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 10.7 mm | 0.4213 | −0.016 mm |
| 10.8 mm | 0.4252 | +0.084 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| 13/32" | Fractional | 0.4062 | 10.32 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 27/64" | Fractional | 0.4219 | 10.72 |
| 7/16" | Fractional | 0.4375 | 11.11 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| 1/2-13 UNC | 27/64 | 78 |
| M12 × 1.25 | 10.8 mm | 79 |
| M12 × 1.5 | 10.5 mm | 66 |
| M12 × 1.75 | 10.2 mm | 56 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| 3/8" bolt | 0.3750" | 0.0469" | 0.0234" | – |
| M10 bolt | 10 mm | 0.72 mm | 0.36 mm | Close fit (close 10.5, normal 11 mm) |


## FAQ

**What size is a 27/64 in drill?**
A 27/64 in drill is 0.4219 in, which is 10.72 mm (10.7156 mm exactly).

**What is the metric equivalent of a 27/64 in drill?**
The nearest metric drill is 10.7 mm, 0.016 mm smaller. The other close size is 10.8 mm.

**What tap uses a 27/64 in drill?**
A 27/64 in drill is the standard tap drill for 1/2-13 UNC (about 78 % thread).

**Which number or letter drill is closest to 27/64 in?**
Letter Z (0.4130 in) is the closest, 0.0089 in smaller.

**What does a 27/64 in drill clear?**
It clears a M10 bolt with 0.72 mm total clearance (0.36 mm per side); for metric bolts: close fit.

Source page: https://machinistcharts.com/drill-size/27-64-inch/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)