Letter Z drill size
A letter Z drill is 0.4130 in (10.49 mm). It is the largest letter drill on this chart; the nearest metric drill is 10.5 mm.
Letter Z 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 |
|---|---|---|---|---|
| 10.4 mm | 0.4094" | −0.090 mm | −0.0036" | Smaller |
| 10.5 mm | 0.4134" | +0.010 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 Letter Z 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 |
|---|---|---|---|
| M12 × 1.5 | 10.5 mm | 77 % | Soft metals, plastics |
| M12 × 1.75 | 10.2 mm | 66 % | Good in steel |
Clearance for screws and bolts
Bolts and screws a Letter Z 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 |
|---|---|---|---|---|
| 3/8" bolt | 0.3750" | 0.0380" | 0.0190" | – |
| M10 bolt | 10 mm | 0.49 mm | 0.25 mm | Tighter than close fit (10.5 mm) |
Inch clearance is the drill size minus the basic major diameter. A drilled hole usually cuts slightly oversize.
Letter drill index
Every size in the series, holes drawn to scale.
Common questions
What size is a letter Z drill?
A letter Z drill is 0.4130 in, which is 10.49 mm (10.4902 mm exactly).
What is the metric equivalent of a letter Z drill?
The nearest metric drill is 10.5 mm, 0.010 mm larger. The other close size is 10.4 mm.
What thread can I tap with a letter Z drill?
It leaves about 77 % thread in M12 × 1.5 and 66 % in M12 × 1.75.
Which fractional drill is closest to letter Z?
13/32 in (0.4062 in) is the closest, 0.0067 in smaller.
What does a letter Z drill clear?
It clears a M10 bolt with 0.49 mm total clearance (0.25 mm per side); for metric bolts: tighter than close fit.