# #18 drill size

A #18 drill is 0.1695 in (4.31 mm). It sits between #19 and #17 in the number series; the nearest metric drill is 4.3 mm.

## #18 drill data

- Series: Number drill
- Decimal: 0.1695 in
- Metric: 4.31 mm (4.3053 mm exact)
- Nearest metric drill: 4.3 mm (−0.005 mm)
- Nearest fractional: 11/64" (0.1719 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 4.3 mm | 0.1693 | −0.005 mm |
| 4.4 mm | 0.1732 | +0.095 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| 5/32" | Fractional | 0.1562 | 3.97 |
| #19 | Number | 0.1660 | 4.22 |
| #18 | Number | 0.1695 | 4.31 |
| 11/64" | Fractional | 0.1719 | 4.37 |
| #17 | Number | 0.1730 | 4.39 |
| Letter A | Letter | 0.2340 | 5.94 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| M5 × 0.8 | 4.2 mm | 67 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| #4 screw | 0.1120" | 0.0575" | 0.0288" | – |
| #5 screw | 0.1250" | 0.0445" | 0.0223" | – |
| #6 screw | 0.1380" | 0.0315" | 0.0158" | – |
| M4 bolt | 4 mm | 0.31 mm | 0.15 mm | Close fit (close 4.3, normal 4.5 mm) |
| #8 screw | 0.1640" | 0.0055" | 0.0028" | – |


## FAQ

**What size is a #18 drill?**
A #18 drill is 0.1695 in, which is 4.31 mm (4.3053 mm exactly).

**What is the metric equivalent of a #18 drill?**
The nearest metric drill is 4.3 mm, 0.005 mm smaller. The other close size is 4.4 mm.

**What thread can I tap with a #18 drill?**
It leaves about 67 % thread in M5 × 0.8.

**Which fractional drill is closest to #18?**
11/64 in (0.1719 in) is the closest, 0.0024 in larger.

**What does a #18 drill clear?**
It clears a #8 screw with 0.0055" total clearance (0.0028" per side).

Source page: https://machinistcharts.com/drill-size/number-18/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)