# Letter Z drill size

A letter Z drill is 0.4130 in (10.49 mm). It is the largest letter drill on this chart; the nearest metric drill is 10.5 mm.

## Letter Z drill data

- Series: Letter drill
- Decimal: 0.4130 in
- Metric: 10.49 mm (10.4902 mm exact)
- Nearest metric drill: 10.5 mm (+0.010 mm)
- Nearest fractional: 13/32" (0.4062 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 10.4 mm | 0.4094 | −0.090 mm |
| 10.5 mm | 0.4134 | +0.010 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| #1 | Number | 0.2280 | 5.79 |
| Letter Y | Letter | 0.4040 | 10.26 |
| 13/32" | Fractional | 0.4062 | 10.32 |
| Letter Z | Letter | 0.4130 | 10.49 |
| 27/64" | Fractional | 0.4219 | 10.72 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| M12 × 1.5 | 10.5 mm | 77 |
| M12 × 1.75 | 10.2 mm | 66 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| 3/8" bolt | 0.3750" | 0.0380" | 0.0190" | – |
| M10 bolt | 10 mm | 0.49 mm | 0.25 mm | Tighter than close fit (10.5 mm) |


## FAQ

**What size is a letter Z drill?**
A letter Z drill is 0.4130 in, which is 10.49 mm (10.4902 mm exactly).

**What is the metric equivalent of a letter Z drill?**
The nearest metric drill is 10.5 mm, 0.010 mm larger. The other close size is 10.4 mm.

**What thread can I tap with a letter Z drill?**
It leaves about 77 % thread in M12 × 1.5 and 66 % in M12 × 1.75.

**Which fractional drill is closest to letter Z?**
13/32 in (0.4062 in) is the closest, 0.0067 in smaller.

**What does a letter Z drill clear?**
It clears a M10 bolt with 0.49 mm total clearance (0.25 mm per side); for metric bolts: tighter than close fit.

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