5/8-11 Tap Drill Size
The tap drill for 5/8-11 UNC is 17/32 in (0.5313 in, 13.49 mm). That is the standard chart size and leaves about 79% thread.
Drill a 17/32 in hole, then cut the thread with a 5/8-11 tap. The hole is 0.0938 in narrower than the screw, so the tap cuts 0.0469 in into each side.
A full-height thread would be 0.0590 in deep on each side. The 17/32 in drill leaves 79% of that.
Try another material or drill
5/8-11 tap drill size by material
| Material | Target thread | Drill | Size | Thread left |
|---|---|---|---|---|
| Aluminum, brass, plastics | 75% | 17/32 in | 0.5313 in (13.49 mm) | 79% |
| Mild steel | 60% | 35/64 in | 0.5469 in (13.89 mm) | 66% |
| Stainless, titanium | 50% | 9/16 in | 0.5625 in (14.29 mm) | 53% |
The 75% row is the published chart drill. The 60% and 50% rows pick the biggest standard drill that still leaves close to that much thread.
Notes on 5/8-11
At 11 threads per inch, 5/8-11 has a full thread 0.0590 in deep on each side, so one 1/64 in drill step moves the thread by about 13.2 points. 17/32 in leaves 79%, 35/64 in leaves 66% and 9/16 in leaves 53%.
M16 is the nearest metric size, 0.13 mm away, and its pitch is 2.00 mm against 2.309 mm.
How much thread do you need?
The chart prints one drill. The right amount of thread depends on the material, and the guides give slightly different ranges.
| Material | Texas Metalworks | ToolGrit | OSG (tap maker) | Drill for 5/8-11 |
|---|---|---|---|---|
| Aluminum | 70-75% | 60-65% | 65-70% | 17/32 in (79%) to 35/64 in (66%) |
| Brass | 70-75% | 70-75% | 65-70% | 17/32 in (79%) |
| Plastic | not covered | 70-75% | not covered | 17/32 in (79%) |
| Mild steel | 60-65% | 60-65% | 65-70% | 35/64 in (66%) |
| Stainless steel | 50% | 55-60% | 60-70% | 35/64 in (66%) to 9/16 in (53%) |
| Titanium | 50% | 50-55% | not covered | 9/16 in (53%) |
The three rows in the first table follow Texas Metalworks. OSG makes taps, and asks for more thread in stainless than either guide, so its range sits closer to our steel column. ToolGrit also suggests 50 to 55% for blind holes in stainless, titanium and hardened steel, and for small taps (#6 and below).
Why not a full thread?
A 100% thread is not possible in practice. The tap and the thread both have flat crests and roots (ToolGrit).
More thread also means more work for the tap: higher cutting force, more heat, poorer chip clearance and a bigger risk of breaking it (ToolGrit).
And it adds little strength. ToolGrit cites studies showing about 90% of a thread's shear strength at 60% thread. Texas Metalworks says going from 75% to 60% costs only about 5% of pull-out strength.
On 5/8-11, that step is from 17/32 in to 35/64 in. The two drills differ by 0.0156 in.
If you do not have the 17/32 in drill
Here are the drills on either side, and the thread each one leaves.
| Drill | Size | Thread left | What changes |
|---|---|---|---|
| 1/2 in | 0.5000 in (12.70 mm) | 100%+ | Too small, the tap will bind |
| 33/64 in | 0.5156 in (13.10 mm) | 93% | More thread, harder to tap |
| 17/32 in | 0.5313 in (13.49 mm) | 79% | Standard size |
| 35/64 in | 0.5469 in (13.89 mm) | 66% | Less thread, easier to tap |
| 9/16 in | 0.5625 in (14.29 mm) | 53% | Less thread, easier to tap |
A bigger drill removes thread and makes the tap easier to turn. A smaller drill keeps more thread and puts more torque on the tap.
The check behind the 17/32 in number: (0.6250 - 0.5313) / (1.299 x 0.0909) = 79.4%.
What 5/8-11 means
- 5/8
- The major diameter, the widest part of the screw: 0.6250 in (15.88 mm).
- 11
- Threads per inch, so one thread every 0.0909 in (2.309 mm).
- UNC
- Unified National Coarse. Its fine twin is 5/8-18.
The rest of the size, worked out from the major diameter and pitch:
| Property | Value |
|---|---|
| Major diameter | 0.6250 in (15.88 mm) |
| Pitch | 11 TPI (2.309 mm) |
| Pitch diameter (basic) | 0.5660 in (14.38 mm) |
| Minor diameter, internal thread (basic) | 0.5266 in (13.38 mm) |
The pitch and minor diameters are for checking a thread with gauges. You can skip them if you only need the drill.
How long to make the 5/8-11 thread
Aim for a thread at least 1 to 1.5 times the diameter long. ToolGrit's strength figures assume that length.
| Thread length | In threads | Drill a blind hole at least |
|---|---|---|
| 1 x diameter: 0.625 in | 6.9 | 0.989 in |
| 1.5 x diameter: 0.938 in | 10.3 | 1.301 in |
The blind hole depth adds 4 threads (4 x 0.0909 in) so the tap has room to finish and the chips have somewhere to go.
How to tap a 5/8-11 hole
- Drill the hole with the 17/32 in drill (0.5313 in, 13.49 mm).
- For a blind hole, drill 0.989 in deep if you need a 0.625 in thread. That is 4 threads past the thread (ToolGrit).
- Put cutting fluid on the tap. Do not tap dry (ToolGrit, Wikipedia).
- Hold the tap in line with the hole.
- Turn the tap forward, then back it off now and then to break the chip (Wikipedia).
- Need threads right to the bottom of a blind hole? Finish with a bottoming tap (Wikipedia).
Taps usually break for one of these reasons (Wikipedia, ToolGrit):
- Chips clog the flutes.
- The tap is not in line with the hole.
- The tap is pushed too hard or too little.
- There is not enough cutting fluid.
- The drill was too small, so the tap works against too much thread.
Which tap to use for 5/8-11
The three common hand taps differ in how many threads at the tip are tapered (Wikipedia).
- Taper tap: 8 to 10 tapered threads, about 0.7273 in to 0.9091 in on 5/8-11. For hard materials and very small taps.
- Plug tap: 3 to 5 tapered threads, about 0.2727 in to 0.4545 in on 5/8-11. The most common tap, easy to start and keep straight.
- Bottoming tap: 1 to 1.5 tapered threads, about 0.0909 in to 0.1364 in on 5/8-11. Cuts threads to the bottom of a blind hole, usually after a plug tap.
Spiral-point taps are usually used in through holes so the chips can escape. Spiral-flute taps work well in blind holes (Wikipedia).
Forming (roll) taps only work in malleable metals such as mild steel and aluminum (Wikipedia). They use different drill sizes, which we do not cover yet.
5/8-11 vs 5/8-18
These two share the same diameter. They differ in pitch, so they take different drills.
| 5/8-11 | 5/8-18 | |
|---|---|---|
| Series | UNC (coarse) | UNF (fine) |
| Pitch | 11 TPI (2.309 mm) | 18 TPI (1.411 mm) |
| Standard drill | 17/32 in | 37/64 in |
| Thread depth, each side | 0.0590 in (1.50 mm) | 0.0361 in (0.92 mm) |
Thread depth is 0.6495 x pitch. Do not mix the two: a 5/8-11 screw will not fit a 5/8-18 hole.
Closest metric size
M16 is close to 5/8-11, but it is not the same thread.
| Major diameter | Pitch | Standard drill | |
|---|---|---|---|
| 5/8-11 | 15.88 mm | 2.309 mm | 17/32 in |
| M16 | 16.00 mm | 2.000 mm | 14.0 mm |
The diameters differ by 0.13 mm and the pitches are not the same. Do not swap them.
FAQ
What is the tap drill size for 5/8-11?
The standard drill is 17/32 in (0.5313 in, 13.49 mm). It leaves about 79% thread, which is the standard chart choice.
Can I use 35/64 in instead of 17/32 in for 5/8-11?
35/64 in (0.5469 in, 13.89 mm) leaves about 66% thread instead of 79%. The tap cuts more easily and the thread is weaker. That is still at or above the 60% Texas Metalworks suggests for mild steel.
Is a 13.5 mm drill the same as 17/32 in?
It is very close. 13.5 mm is 0.5315 in, against 0.5313 in, 13.49 mm for 17/32 in. It leaves about 79% thread.
What drill size do I use for 5/8-11 in aluminum?
Use 17/32 in (79%) or 35/64 in (66%), depending on the guide. Texas Metalworks says 70 to 75% for soft aluminum, which is 17/32 in. ToolGrit says 60 to 65% for aluminum alloys, which is 35/64 in. Either is a normal choice. OSG, a tap maker, gives 65 to 70% for average work in aluminum, brass and mild steel.
What is the tap drill size for 5/8-11 in stainless steel?
9/16 in (0.5625 in, 14.29 mm) leaves about 53% thread, close to the 50% Texas Metalworks recommends for stainless and titanium. ToolGrit gives 55 to 60% for 304 and 316 stainless, which is between 35/64 in and 9/16 in. The standard drill, 17/32 in, puts more torque on the tap. OSG, a tap maker, asks for 60 to 70% in stainless for average work, which is closer to the steel drill, 35/64 in.
Does a bigger drill make the 5/8-11 thread much weaker?
Not by much at first. ToolGrit cites studies showing about 90% of a thread's shear strength at 60% thread, if the thread is at least 1 to 1.5 times the diameter long. Texas Metalworks says going from 75% to 60% costs only about 5% of pull-out strength. For 5/8-11, the 60% drill is 35/64 in.
How long should a 5/8-11 thread be?
Aim for at least 1 to 1.5 times the diameter, the length ToolGrit's strength figures assume. For 5/8-11 that is 0.625 in to 0.938 in, or about 6.9 to 10.3 threads.
How deep do I drill a blind 5/8-11 hole?
At least 4 threads deeper than the thread you need, says ToolGrit. A 0.625 in thread needs a hole at least 0.989 in deep.
Which tap do I use for a blind 5/8-11 hole?
Start with a plug tap, then finish with a bottoming tap if the thread has to reach the bottom. Wikipedia says a bottoming tap has 1 to 1.5 tapered threads, about 0.0909 in to 0.1364 in on 5/8-11.
What is 5/8-11 in mm?
5/8-11 is 15.88 mm across, with a pitch of 2.309 mm.
Is 5/8-11 a coarse or fine thread?
5/8-11 is a coarse thread (UNC). The fine thread of the same diameter is 5/8-18, which takes 37/64 in.
Related sizes
Chart drill checked against the American Fastener tap and drill chart and the Fabworks tap drill chart. Diameters from Wikipedia: drill bit sizes. Thread percentages, thread length and blind-hole depth from Texas Metalworks and ToolGrit. The percentage formula is the one printed in the OSG tap drill chart, Vol 3 (2024). Tap types and tapping tips from Wikipedia. Last reviewed October 7, 2026.