#40 drill size
A #40 drill is 0.0980 in (2.49 mm). It sits between #41 and #39 in the number series; the nearest metric drill is 2.5 mm.
#40 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 |
|---|---|---|---|---|
| 2.45 mm | 0.0965" | −0.039 mm | −0.0015" | Smaller |
| 2.5 mm | 0.0984" | +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 #40 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).
Clearance for screws and bolts
Bolts and screws a #40 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 |
|---|---|---|---|---|
| #1 screw | 0.0730" | 0.0250" | 0.0125" | – |
| M2 bolt | 2 mm | 0.49 mm | 0.24 mm | Normal fit (normal 2.4, loose 2.6 mm) |
| #2 screw | 0.0860" | 0.0120" | 0.0060" | – |
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 #40 drill?
A #40 drill is 0.0980 in, which is 2.49 mm (2.4892 mm exactly).
What is the metric equivalent of a #40 drill?
The nearest metric drill is 2.5 mm, 0.011 mm larger. The other close size is 2.45 mm.
What thread can I tap with a #40 drill?
It leaves about 79 % thread in M3 × 0.5 and 83 % in #5-40 UNC.
Which fractional drill is closest to #40?
3/32 in (0.0938 in) is the closest, 0.0043 in smaller.
What does a #40 drill clear?
It clears a #2 screw with 0.0120" total clearance (0.0060" per side).