Letter J drill size
A letter J drill is 0.2770 in (7.04 mm). It sits between letter I and letter K in the letter series; the nearest metric drill is 7.0 mm.
Letter J 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 |
|---|---|---|---|---|
| 7.0 mm | 0.2756" | −0.036 mm | −0.0014" | Smaller |
| 7.1 mm | 0.2795" | +0.064 mm | +0.0025" | 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 | −0.0490" |
| 17/64" | Fractional | 0.2656" | 6.75 mm | −0.0114" |
| Letter I | Letter | 0.2720" | 6.91 mm | −0.0050" |
| Letter J | Letter | 0.2770" | 7.04 mm | this size |
| Letter K | Letter | 0.2810" | 7.14 mm | +0.0040" |
| 9/32" | Fractional | 0.2812" | 7.14 mm | +0.0042" |
Threads a Letter J drill can tap
Threads from the tap tables on this site that this drill can tap, with the thread percentage it leaves (55–85 % shown).
| Thread | Standard drill | Thread with this drill | Suits |
|---|---|---|---|
| M8 × 1 | 7 mm | 74 % | Good in steel |
| 5/16-24 UNF | I | 66 % | Good in steel |
| M8 × 1.25 | 6.8 mm | 59 % | Hard, tough metals |
Clearance for screws and bolts
Bolts and screws a Letter J 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 |
|---|---|---|---|---|
| #12 screw | 0.2160" | 0.0610" | 0.0305" | – |
| 1/4" bolt | 0.2500" | 0.0270" | 0.0135" | – |
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 J drill?
A letter J drill is 0.2770 in, which is 7.04 mm (7.0358 mm exactly).
What is the metric equivalent of a letter J drill?
The nearest metric drill is 7.0 mm, 0.036 mm smaller. The other close size is 7.1 mm.
What thread can I tap with a letter J drill?
It leaves about 74 % thread in M8 × 1 and 66 % in 5/16-24 UNF.
Which fractional drill is closest to letter J?
9/32 in (0.2812 in) is the closest, 0.0042 in larger.
What does a letter J drill clear?
It clears a 1/4" bolt with 0.0270" total clearance (0.0135" per side).