#20 drill size
A #20 drill is 0.1610 in (4.09 mm). It sits between #21 and #19 in the number series; the nearest metric drill is 4.1 mm.
#20 at a glance
Decimal, metric and the nearest sizes in the other series.
Nearest metric drills
Metric drills step by 0.05 mm below 3 mm and by 0.1 mm from 3 mm. Difference is metric minus inch size.
| Metric drill | Inch | Difference | In inches | Hole |
|---|---|---|---|---|
| 4.0 mm | 0.1575" | −0.089 mm | −0.0035" | Smaller |
| 4.1 mm | 0.1614" | +0.011 mm | +0.0004" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
Threads a #20 drill can tap
Threads from the tap tables on this site that this drill can tap, with the thread percentage it leaves (55–85 % shown).
| Thread | Standard drill | Thread with this drill | Suits |
|---|---|---|---|
| #10-32 UNF | #21 | 71 % | Good in steel |
Clearance for screws and bolts
Bolts and screws a #20 hole clears, with the diametral clearance and the gap each side. Metric sizes are compared with ISO 273.
| Fastener | Diameter | Clearance | Per side | ISO 273, metric only |
|---|---|---|---|---|
| #3 screw | 0.0990" | 0.0620" | 0.0310" | – |
| #4 screw | 0.1120" | 0.0490" | 0.0245" | – |
| #5 screw | 0.1250" | 0.0360" | 0.0180" | – |
| M3.5 bolt | 3.5 mm | 0.59 mm | 0.29 mm | Normal fit (normal 3.9, loose 4.2 mm) |
| #6 screw | 0.1380" | 0.0230" | 0.0115" | – |
| M4 bolt | 4 mm | 0.09 mm | 0.04 mm | Tighter than close fit (4.3 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Number drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a #20 drill?
A #20 drill is 0.1610 in, which is 4.09 mm (4.0894 mm exactly).
What is the metric equivalent of a #20 drill?
The nearest metric drill is 4.1 mm, 0.011 mm larger. The other close size is 4.0 mm.
What thread can I tap with a #20 drill?
It leaves about 71 % thread in #10-32 UNF.
Which fractional drill is closest to #20?
5/32 in (0.1562 in) is the closest, 0.0048 in smaller.
What does a #20 drill clear?
It clears a M4 bolt with 0.09 mm total clearance (0.04 mm per side); for metric bolts: tighter than close fit.