S drill bit size
0.348 in
8.84 mm · letter drill
| Inches | 0.348 in |
| Millimetres | 8.84 mm |
| Nearest metric drill | 8.8 mm |
| System | Letter (A to Z) |
What S means
A bit marked S 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 S:
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.12 in smaller |
| fractional | 11/32" — 0.3438 in | 0.0042 in smaller |
| metric | 8.8 mm | 0.039 mm smaller |
The closest substitute is 0.0042 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 0.348 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 |
|---|---|---|
| Q | 0.332 in | 8.43 mm |
| R | 0.339 in | 8.61 mm |
| 11/32" | 0.3438 in | 8.73 mm |
| S | 0.348 in | 8.84 mm |
| T | 0.358 in | 9.09 mm |
| 23/64" | 0.3594 in | 9.13 mm |
| U | 0.368 in | 9.35 mm |
Frequently asked questions
What size is a S drill bit?
0.348 inches, which is 8.84 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 S drill bit in mm?
8.84 mm. A metric index will offer 8.8 mm as the nearest stocked size, which is 0.039 mm smaller — enough to matter when tapping and not enough to matter for a clearance hole.
Is S 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 S?
T at 0.358 inches — 0.01 inches larger. Below it is 11/32" at 0.3438.
Other sizes
- T drill bit — 0.358 in, 9.09 mm
- 23/64" drill bit — 0.3594 in, 9.13 mm
- U drill bit — 0.368 in, 9.35 mm
- 3/8" drill bit — 0.375 in, 9.52 mm
- V drill bit — 0.377 in, 9.58 mm
- W drill bit — 0.386 in, 9.8 mm
- 25/64" drill bit — 0.3906 in, 9.92 mm
- X drill bit — 0.397 in, 10.08 mm