Y drill bit size
0.404 in
10.26 mm · letter drill
| Inches | 0.404 in |
| Millimetres | 10.26 mm |
| Nearest metric drill | 10.3 mm |
| System | Letter (A to Z) |
What Y means
A bit marked Y is a letter drill. Letters run A to Z and get larger as they advance, covering 0.234 to 0.413 inches — the gap between the largest number drill and the point where fractional sizes become fine enough to be useful.
The same hole in the other systems
Three drill systems overlap across this range and a workshop rarely has all three. The nearest bit of each other kind to Y:
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.176 in smaller |
| fractional | 13/32" — 0.4063 in | 0.0022 in larger |
| metric | 10.3 mm | 0.038 mm larger |
One of those is within three thousandths of an inch, which is inside the tolerance of most hand-held work — substitute it and nobody will know.
What gets drilled at 0.404 inches
Clearance holes for bolts up to about half an inch, and tapping drills for the larger unified threads. Above a quarter inch a hand drill starts to want two hands and a slower speed, and the bit wants a pilot hole.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| W | 0.386 in | 9.8 mm |
| 25/64" | 0.3906 in | 9.92 mm |
| X | 0.397 in | 10.08 mm |
| Y | 0.404 in | 10.26 mm |
| 13/32" | 0.4063 in | 10.32 mm |
| Z | 0.413 in | 10.49 mm |
| 27/64" | 0.4219 in | 10.72 mm |
Frequently asked questions
What size is a Y drill bit?
0.404 inches, which is 10.26 mm. Letter drills run A to Z and get larger as the letter advances, filling the gap between the largest number drill and the fractional sizes.
What is a Y drill bit in mm?
10.26 mm. A metric index will offer 10.3 mm as the nearest stocked size, which is 0.038 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is Y a tapping drill size?
Not for any of the unified threads on this site. It sits between the sizes the standard taps call for, so it is a clearance or pilot drill rather than a tapping one.
What is the next size up from Y?
13/32" at 0.4063 inches — 0.0022 inches larger. Below it is X at 0.397.
Other sizes
- 13/32" drill bit — 0.4063 in, 10.32 mm
- Z drill bit — 0.413 in, 10.49 mm
- 27/64" drill bit — 0.4219 in, 10.72 mm
- 7/16" drill bit — 0.4375 in, 11.11 mm
- 29/64" drill bit — 0.4531 in, 11.51 mm
- 15/32" drill bit — 0.4688 in, 11.91 mm
- 31/64" drill bit — 0.4844 in, 12.3 mm
- 1/2" drill bit — 0.5 in, 12.7 mm