# Letter C drill size

A letter C drill is 0.2420 in (6.15 mm). It sits between letter B and letter D in the letter series; the nearest metric drill is 6.1 mm.

## Letter C drill data

- Series: Letter drill
- Decimal: 0.2420 in
- Metric: 6.15 mm (6.1468 mm exact)
- Nearest metric drill: 6.1 mm (−0.047 mm)
- Nearest fractional: 15/64" (0.2344 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 6.1 mm | 0.2402 | −0.047 mm |
| 6.2 mm | 0.2441 | +0.053 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| 15/64" | Fractional | 0.2344 | 5.95 |
| Letter B | Letter | 0.2380 | 6.05 |
| Letter C | Letter | 0.2420 | 6.15 |
| Letter D | Letter | 0.2460 | 6.25 |
| 1/4" | Fractional | 0.2500 | 6.35 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| #10 screw | 0.1900" | 0.0520" | 0.0260" | – |
| #12 screw | 0.2160" | 0.0260" | 0.0130" | – |
| M6 bolt | 6 mm | 0.15 mm | 0.07 mm | Tighter than close fit (6.4 mm) |


## FAQ

**What size is a letter C drill?**
A letter C drill is 0.2420 in, which is 6.15 mm (6.1468 mm exactly).

**What is the metric equivalent of a letter C drill?**
The nearest metric drill is 6.1 mm, 0.047 mm smaller. The other close size is 6.2 mm.

**Which fractional drill is closest to letter C?**
15/64 in (0.2344 in) is the closest, 0.0076 in smaller.

**What does a letter C drill clear?**
It clears a M6 bolt with 0.15 mm total clearance (0.07 mm per side); for metric bolts: tighter than close fit.

Source page: https://machinistcharts.com/drill-size/letter-c/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)