E drill bit size
0.25 in
6.35 mm · letter drill
| Inches | 0.25 in |
| Millimetres | 6.35 mm |
| Nearest metric drill | 6.4 mm |
| System | Letter (A to Z) |
What E means
A bit marked E 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.
E and 1/4" are the same bit
E and 1/4" are both exactly 0.25 inches. This is the one place in the three imperial systems where a letter drill and a fractional drill land on the same diameter, so a bit marked either way cuts the same hole. If you have both in a drawer, you have two of the same drill.
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 E:
| System | Nearest size | Difference |
|---|---|---|
| number | #1 — 0.228 in | 0.022 in smaller |
| fractional | 1/4" — 0.25 in | identical |
| metric | 6.4 mm | 0.05 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 0.25 inches
Where the quarter-inch and five-sixteenths taps are drilled, and where clearance holes for small bolts begin. The three drill systems overlap most densely across this band, which is why a bit here is the one most often picked up and misidentified.
Either side of it
| Drill | Inches | Millimetres |
|---|---|---|
| B | 0.238 in | 6.05 mm |
| C | 0.242 in | 6.15 mm |
| D | 0.246 in | 6.25 mm |
| E | 0.25 in | 6.35 mm |
| 1/4" | 0.25 in | 6.35 mm |
| F | 0.257 in | 6.53 mm |
| G | 0.261 in | 6.63 mm |
Frequently asked questions
What size is a E drill bit?
0.25 inches, which is 6.35 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 E drill bit in mm?
6.35 mm. A metric index will offer 6.4 mm as the nearest stocked size, which is 0.05 mm larger — enough to matter when tapping and not enough to matter for a clearance hole.
Is E a tapping drill size?
Not for any of the unified threads on this site. The next size up, F, is the tapping drill for 5/16-18.
What is the next size up from E?
F at 0.257 inches — 0.007 inches larger. Below it is D at 0.246.
Other sizes
- 1/4" drill bit — 0.25 in, 6.35 mm
- F drill bit — 0.257 in, 6.53 mm
- G drill bit — 0.261 in, 6.63 mm
- 17/64" drill bit — 0.2656 in, 6.75 mm
- H drill bit — 0.266 in, 6.76 mm
- I drill bit — 0.272 in, 6.91 mm
- J drill bit — 0.277 in, 7.04 mm
- K drill bit — 0.281 in, 7.14 mm