A letter u drill measures 0.3680 inch (9.347 mm). The closest fractional drill is 3/8" (0.3750") and the closest metric drill is 9.3 mm (0.3661"). It is the standard tap drill for 7/16-14.
What are the letter u drill equivalents?
| Drill | System | Decimal (in) | mm | Difference (in) |
|---|---|---|---|---|
| U | letter | 0.3680 | 9.347 | 0 |
| 9.3 mm | metric | 0.3661 | 9.300 | -0.0019 |
| 9.4 mm | metric | 0.3701 | 9.400 | +0.0021 |
Tap drill for: 7/16-14.
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 u drill run?
| Material | RPM (HSS) | Feed (in/rev) |
|---|---|---|
| 6061-T6 aluminum | 2,076 | 0.0074 |
| 360 free-machining brass | 1,557 | 0.0066 |
| 1018 cold rolled steel | 830 | 0.0055 |
| 304 stainless steel | 415 | 0.0037 |
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 u drill in inches?
0.3680 inch, which is 9.347 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, 9.3 mm is within 0.0019 inch.
What tap uses a letter u drill?
It is the standard 75% thread tap drill for 7/16-14. Tap drills are chosen to leave about 75% of full thread depth, the balance of strength and tapping torque that published charts use.