# #28 drill size

A #28 drill is 0.1405 in (3.57 mm). It sits between #29 and #27 in the number series; the nearest metric drill is 3.6 mm.

## #28 drill data

- Series: Number drill
- Decimal: 0.1405 in
- Metric: 3.57 mm (3.5687 mm exact)
- Nearest metric drill: 3.6 mm (+0.031 mm)
- Nearest fractional: 9/64" (0.1406 in)

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 3.5 mm | 0.1378 | −0.069 mm |
| 3.6 mm | 0.1417 | +0.031 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| 1/8" | Fractional | 0.1250 | 3.17 |
| #29 | Number | 0.1360 | 3.45 |
| #28 | Number | 0.1405 | 3.57 |
| 9/64" | Fractional | 0.1406 | 3.57 |
| #27 | Number | 0.1440 | 3.66 |
| Letter A | Letter | 0.2340 | 5.94 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| M4 × 0.5 | 3.5 mm | 66 |
| #8-36 UNF | #29 | 65 |
| #8-32 UNC | #29 | 58 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| #2 screw | 0.0860" | 0.0545" | 0.0273" | – |
| #3 screw | 0.0990" | 0.0415" | 0.0208" | – |
| #4 screw | 0.1120" | 0.0285" | 0.0143" | – |
| M3 bolt | 3 mm | 0.57 mm | 0.28 mm | Normal fit (normal 3.4, loose 3.6 mm) |
| #5 screw | 0.1250" | 0.0155" | 0.0078" | – |
| M3.5 bolt | 3.5 mm | 0.07 mm | 0.03 mm | Tighter than close fit (3.7 mm) |
| #6 screw | 0.1380" | 0.0025" | 0.0013" | – |


## FAQ

**What size is a #28 drill?**
A #28 drill is 0.1405 in, which is 3.57 mm (3.5687 mm exactly).

**What is the metric equivalent of a #28 drill?**
The nearest metric drill is 3.6 mm, 0.031 mm larger. The other close size is 3.5 mm.

**What thread can I tap with a #28 drill?**
It leaves about 66 % thread in M4 × 0.5 and 65 % in #8-36 UNF.

**Which fractional drill is closest to #28?**
9/64 in (0.1406 in) is the closest, 0.0001 in larger.

**What does a #28 drill clear?**
It clears a #6 screw with 0.0025" total clearance (0.0013" per side).

Source page: https://machinistcharts.com/drill-size/number-28/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)