# #50 drill size

A #50 drill is 0.0700 in (1.78 mm). It is the standard tap drill for #2-56 UNC and #2-64 UNF; the nearest metric drill is 1.8 mm.

## #50 drill data

- Series: Number drill
- Decimal: 0.0700 in
- Metric: 1.78 mm (1.7780 mm exact)
- Nearest metric drill: 1.8 mm (+0.022 mm)
- Nearest fractional: 1/16" (0.0625 in)
- Standard tap drill for: #2-56 UNC, #2-64 UNF

## Nearest metric drills

| Metric drill | Inch | Difference |
|---|---|---|
| 1.75 mm | 0.0689 | −0.028 mm |
| 1.8 mm | 0.0709 | +0.022 mm |

## Nearby inch drills

| Drill | Series | Inch | mm |
|---|---|---|---|
| 1/16" | Fractional | 0.0625 | 1.59 |
| #51 | Number | 0.0670 | 1.70 |
| #50 | Number | 0.0700 | 1.78 |
| #49 | Number | 0.0730 | 1.85 |
| 5/64" | Fractional | 0.0781 | 1.98 |
| Letter A | Letter | 0.2340 | 5.94 |

## Threads this drill can tap

| Thread | Standard drill | Thread % with this drill |
|---|---|---|
| #2-64 UNF | #50 | 79 |
| #2-56 UNC | #50 | 69 |

## Clearance

| Fastener | Diameter | Clearance | Per side | ISO 273 |
|---|---|---|---|---|
| M1.6 bolt | 1.6 mm | 0.18 mm | 0.09 mm | Close fit (close 1.7, normal 1.8 mm) |


## FAQ

**What size is a #50 drill?**
A #50 drill is 0.0700 in, which is 1.78 mm (1.7780 mm exactly).

**What is the metric equivalent of a #50 drill?**
The nearest metric drill is 1.8 mm, 0.022 mm larger. The other close size is 1.75 mm.

**What tap uses a #50 drill?**
A #50 drill is the standard tap drill for #2-56 UNC (about 69 % thread) and #2-64 UNF (about 79 % thread).

**Which fractional drill is closest to #50?**
1/16 in (0.0625 in) is the closest, 0.0075 in smaller.

**What does a #50 drill clear?**
It clears a M1.6 bolt with 0.18 mm total clearance (0.09 mm per side); for metric bolts: close fit.

Source page: https://machinistcharts.com/drill-size/number-50/
Updated: 2026-10-06
Publisher: MachinistCharts (https://machinistcharts.com)