# #23 drill size

A #23 drill is 0.1540 in (3.91 mm). It sits between #24 and #22 in the number series; the nearest metric drill is 3.9 mm.

## #23 drill data

- Series: Number drill
- Decimal: 0.1540 in
- Metric: 3.91 mm (3.9116 mm exact)
- Nearest metric drill: 3.9 mm (−0.012 mm)
- Nearest fractional: 5/32" (0.1562 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 3.9 mm | 0.1535 | −0.012 mm |
| 4.0 mm | 0.1575 | +0.088 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| 9/64" | Fractional | 0.1406 | 3.57 |
| #24 | Number | 0.1520 | 3.86 |
| #23 | Number | 0.1540 | 3.91 |
| 5/32" | Fractional | 0.1562 | 3.97 |
| #22 | Number | 0.1570 | 3.99 |
| Letter A | Letter | 0.2340 | 5.94 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| #10-24 UNC | #25 | 67 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| #3 screw | 0.0990" | 0.0550" | 0.0275" | – |
| #4 screw | 0.1120" | 0.0420" | 0.0210" | – |
| #5 screw | 0.1250" | 0.0290" | 0.0145" | – |
| M3.5 bolt | 3.5 mm | 0.41 mm | 0.21 mm | Normal fit (normal 3.9, loose 4.2 mm) |
| #6 screw | 0.1380" | 0.0160" | 0.0080" | – |


## FAQ

**What size is a #23 drill?**
A #23 drill is 0.1540 in, which is 3.91 mm (3.9116 mm exactly).

**What is the metric equivalent of a #23 drill?**
The nearest metric drill is 3.9 mm, 0.012 mm smaller. The other close size is 4.0 mm.

**What thread can I tap with a #23 drill?**
It leaves about 67 % thread in #10-24 UNC.

**Which fractional drill is closest to #23?**
5/32 in (0.1562 in) is the closest, 0.0023 in larger.

**What does a #23 drill clear?**
It clears a #6 screw with 0.0160" total clearance (0.0080" per side).

Source page: https://machinistcharts.com/drill-size/number-23/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)