Tap drill size for 7/16-14
U
0.368 inches · 9.35 mm · 75% thread engagement
| Tap drill (75% thread) | U — 0.368" / 9.35 mm |
| Major diameter | 0.4375" / 11.11 mm |
| Drill for a 100% thread | 0.3447" / 8.76 mm |
| Threads per inch | 14 |
| Pitch | 0.0714" / 1.81 mm |
| Series | UNC (coarse) |
Where the number comes from
A tap cuts the thread; the drill leaves the hole it cuts into. Cutting the full thread form would mean drilling the major diameter less the whole height of the thread:
0.4375 − 1.299 ÷ 14 = 0.3447 inches
That is the 100% thread, which nobody drills — the tap has to remove every scrap of metal and usually breaks trying. Charts give 75%, so three quarters of the thread height is cut away and the rest is left as clearance:
0.4375 − 0.974 ÷ 14 = 0.3679 inches
The nearest drill that actually exists is U at 0.368 inches, which is 0.0001 inches over the theoretical figure. That is the number printed on every 7/16-14 tap chart, and this is where it comes from.
The same hole at other engagements
Thread engagement is a choice, not a constant. Less engagement means an easier cut and a longer tap life for very little loss of strength, which is why a machinist working stainless will not drill the chart size.
| Engagement | Theoretical | Drill | Millimetres |
|---|---|---|---|
| 50% | 0.3911" | 25/64" (0.3906") | 9.92 mm |
| 65% | 0.3772" | V (0.377") | 9.58 mm |
| 75% — the chart value | 0.3679" | U (0.368") | 9.35 mm |
| 85% | 0.3586" | T (0.358") | 9.09 mm |
A 75% thread is close to the practical ceiling: going from 75% to 100% adds only a few per cent of strength and roughly doubles the torque needed to turn the tap. Going the other way, a 65% thread still holds about 95% of the load a 75% thread does, which is why 65% is the usual choice in anything harder than mild steel.
7/16-14 in metric
7/16-14 has a major diameter of 11.11 mm and a pitch of 1.81 mm. The nearest metric tap is M12 at 12 mm, which is 0.89 mm larger — far enough apart that there is no confusing the two. An M12 bolt will not enter a 7/16-14 hole at all, so if a fastener nearly fits, neither of these is the standard you are looking for.
For the drill itself the conversion is straightforward: U is 9.35 mm, and a metric drill index will offer 9.3 mm as the nearest size.
What 7/16-14 is used for
Structural bolting and heavy machinery.
The same 0.4375" screw is also made as 7/16-20, the fine version, which takes a 25/64" drill instead. Coarse threads tap faster, tolerate damage better and hold better in soft material.
Frequently asked questions
What size drill bit do I need for a 7/16-14 tap?
A U drill, which is 0.368 inches or 9.35 mm. That is the standard 75% thread engagement figure, and it is what every published tap chart gives for 7/16-14.
What size hole do I need for a 7/16-14 thread?
The same U hole — 0.368 inches. The number comes from subtracting the thread height from the major diameter: 0.4375 − 0.974 ÷ 14 = 0.3679 inches, and U is the nearest drill that exists.
What is the 7/16-14 tap drill size in mm?
9.35 mm. There is no metric drill of exactly that size, so a metric drill index gives you 9.3 mm as the nearest — close enough for 7/16-14 in most materials, though it changes the thread engagement slightly.
Can I use a V instead?
Yes, and in hard material you should. V gives about 65% thread engagement instead of 75%. That costs very little strength — a 65% thread holds roughly 95% of what a 75% thread does — and it makes the tap markedly easier to turn, which is the trade every machinist makes in stainless or tough alloy.
Other tap sizes
- 7/16-20 tap drill size — 25/64"
- 1/2-13 tap drill size — 27/64"
- 1/2-20 tap drill size — 29/64"
- 9/16-12 tap drill size — 31/64"
- 9/16-18 tap drill size — 33/64"
- 5/8-11 tap drill size — 17/32"
- 5/8-18 tap drill size — 37/64"
- 3/4-10 tap drill size — 21/32"
- 3/4-16 tap drill size — 11/16"
- 7/8-9 tap drill size — 49/64"