Letter D drill size
A letter D drill is 0.2460 in (6.25 mm). It sits between letter C and letter E in the letter series; the nearest metric drill is 6.2 mm.
Letter D 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 |
|---|---|---|---|---|
| 6.2 mm | 0.2441" | −0.048 mm | −0.0019" | Smaller |
| 6.3 mm | 0.2480" | +0.052 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 | −0.0180" |
| 15/64" | Fractional | 0.2344" | 5.95 mm | −0.0116" |
| Letter C | Letter | 0.2420" | 6.15 mm | −0.0040" |
| Letter D | Letter | 0.2460" | 6.25 mm | this size |
| 1/4" | Fractional | 0.2500" | 6.35 mm | +0.0040" |
| Letter E | Letter | 0.2500" | 6.35 mm | +0.0040" |
Threads a Letter D 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 D 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" | 0.0560" | 0.0280" | – |
| #12 screw | 0.2160" | 0.0300" | 0.0150" | – |
| M6 bolt | 6 mm | 0.25 mm | 0.12 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 D drill?
A letter D drill is 0.2460 in, which is 6.25 mm (6.2484 mm exactly).
What is the metric equivalent of a letter D drill?
The nearest metric drill is 6.2 mm, 0.048 mm smaller. The other close size is 6.3 mm.
Which fractional drill is closest to letter D?
1/4 in (0.2500 in) is the closest, 0.0040 in larger.
What does a letter D drill clear?
It clears a M6 bolt with 0.25 mm total clearance (0.12 mm per side); for metric bolts: tighter than close fit.