A letter j drill measures 0.2770 inch (7.036 mm). The closest fractional drill is 9/32" (0.2813") and the closest metric drill is 7.0 mm (0.2756").
What are the letter j drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| J | letter | 0.2770 | 7.036 | 0 |
| 7.0 mm | metric | 0.2756 | 7.000 | -0.0014 |
| 7.1 mm | metric | 0.2795 | 7.100 | +0.0025 |
Drill sets that include this size
Number and letter sizes come in indexed sets; buy the set rather than single drills.
What speed should a letter j drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 2,758 | 0.0055 |
| 360 free-machining brass | 2,068 | 0.0050 |
| 1018 cold rolled steel | 1,103 | 0.0042 |
| 304 stainless steel | 552 | 0.0028 |
Starting points from conservative HSS drilling speeds. Small drills often call for more RPM than a benchtop drill press offers; run at the top speed and feed gently. Use cutting oil in steel and stainless, and clamp the work: never hold it by hand.
Cutting fluid for drilling
Frequently asked questions
What is a letter j drill in inches?
0.2770 inch, which is 7.036 mm. Letter drills run from A (0.234 inch) to Z (0.413 inch), continuing upward from the number drills. If you do not have this exact size, 7.0 mm is within 0.0014 inch.
What tap uses a letter j drill?
No common UNC or UNF thread uses it as its standard 75% tap drill, but it often serves as an alternative drill for a slightly different percentage of thread, or as a clearance or pilot size. The tap drill chart lists every standard pairing.