Letter E drill size
A letter E drill is 0.2500 in (6.35 mm). It is the same size as a 1/4 in drill; the nearest metric drills are 6.3 and 6.4 mm, equally close.
Letter E 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 |
|---|---|---|---|---|
| 6.3 mm | 0.2480" | −0.050 mm | −0.0020" | Smaller |
| 6.4 mm | 0.2520" | +0.050 mm | +0.0020" | Larger |
Nearby inch drills
The next size down and up in each inch series, so you can pick a substitute from the drawer.
| Drill | Series | Inch | mm | Difference |
|---|---|---|---|---|
| #1 | Number | 0.2280" | 5.79 mm | −0.0220" |
| 15/64" | Fractional | 0.2344" | 5.95 mm | −0.0156" |
| Letter D | Letter | 0.2460" | 6.25 mm | −0.0040" |
| 1/4" | Fractional | 0.2500" | 6.35 mm | 0" |
| Letter E | Letter | 0.2500" | 6.35 mm | this size |
| Letter F | Letter | 0.2570" | 6.53 mm | +0.0070" |
| 17/64" | Fractional | 0.2656" | 6.75 mm | +0.0156" |
Threads a Letter E drill can tap
No thread in the tap tables on this site falls between 55 and 85 % thread with this drill, so it is not a useful tap drill for them. Drills this size are mostly used for clearance, pilot and pin holes.
Clearance for screws and bolts
Bolts and screws a Letter E 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 |
|---|---|---|---|---|
| #10 screw | 0.1900" | 0.0600" | 0.0300" | – |
| #12 screw | 0.2160" | 0.0340" | 0.0170" | – |
| M6 bolt | 6 mm | 0.35 mm | 0.17 mm | Tighter than close fit (6.4 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 E drill?
A letter E drill is 0.2500 in, which is 6.35 mm (6.3500 mm exactly).
What is the metric equivalent of a letter E drill?
The nearest metric drill is 6.3 mm, 0.050 mm smaller. The other close size is 6.4 mm.
Which fractional drill is closest to letter E?
1/4 in (0.2500 in) is the closest, 0.0000 in smaller.
Is a letter E drill the same as a 1/4 in drill?
Yes. Both are 0.2500 in (6.35 mm).
What does a letter E drill clear?
It clears a M6 bolt with 0.35 mm total clearance (0.17 mm per side); for metric bolts: tighter than close fit.