W drill bit size
0.386 in
9.8 mm · letter drill
| Inches | 0.386 in |
| Millimetres | 9.8 mm |
| Nearest metric drill | 9.8 mm |
| System | Letter (A to Z) |
What W means
A bit marked W 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 W:
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.158 in smaller |
| fractional | 25/64" — 0.3906 in | 0.0046 in larger |
| metric | 9.8 mm | identical |
The closest substitute is 0.0046 inches away. For a clearance hole that is nothing; for a tapping hole it moves the thread engagement by several per cent, which is the difference between an easy tap and a broken one.
What gets drilled at 0.386 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 |
|---|---|---|
| U | 0.368 in | 9.35 mm |
| 3/8" | 0.375 in | 9.52 mm |
| V | 0.377 in | 9.58 mm |
| 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 |
Frequently asked questions
What size is a W drill bit?
0.386 inches, which is 9.8 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 W drill bit in mm?
9.8 mm. A metric index will offer 9.8 mm as the nearest stocked size, which is near enough identical.
Is W a tapping drill size?
Not for any of the unified threads on this site. The next size up, 25/64", is the tapping drill for 7/16-20.
What is the next size up from W?
25/64" at 0.3906 inches — 0.0046 inches larger. Below it is V at 0.377.
Other sizes
- 25/64" drill bit — 0.3906 in, 9.92 mm
- X drill bit — 0.397 in, 10.08 mm
- Y drill bit — 0.404 in, 10.26 mm
- 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