The tap drill for 5/8-11 UNC is 17/32" (0.5312 in, 13.49 mm), which gives about 79% of full thread depth. The exact 75% hole is 0.5364 in (13.63 mm). The table lists every number, letter, fractional and metric drill that gives between 55% and 90% thread, so you can work from the bits you own.
| Drill | Type | in | mm | Thread | Note |
|---|---|---|---|---|---|
| 13.4 mm | metric | 0.5276 | 13.40 | 83% | deep, hard to tap |
| 17/32" | fraction | 0.5312 | 13.49 | 79% | chart drill |
| 13.5 mm | metric | 0.5315 | 13.50 | 79% | |
| 13.6 mm | metric | 0.5354 | 13.60 | 76% | |
| 13.7 mm | metric | 0.5394 | 13.70 | 73% | |
| 13.8 mm | metric | 0.5433 | 13.80 | 69% | |
| 35/64" | fraction | 0.5469 | 13.89 | 66% | easier to tap |
About the 5/8-11 thread
5/8-11 is the coarse 5/8 in thread: hex bolts, threaded rod and anchor rods, and the spindle thread of most angle grinders sold in North America, which is why grinder wheels, cup brushes, core bits and backing pads are sold “5/8-11”. In building work 5/8 in threaded rod and anchors appear where loads are heavier than a 1/2 in bolt is meant for.
17/32 in (0.531 in) is the chart drill at about 79% thread. 35/64 in gives about 66% and is easier to turn by hand; 13.6 mm (0.535 in) is the close metric option. At this size, drill in stages and keep the part rigid, because a large tap that is not square to the hole cuts a poor thread and is easy to break.
5/8-11 thread dimensions
| Dimension | Value | Also |
|---|---|---|
| Nominal diameter | 0.6250 in | 15.88 mm |
| Threads per inch | 11 | pitch 0.0909 in (2.309 mm) |
| Basic pitch diameter | 0.5660 in | 14.375 mm |
| Basic minor diameter (nut) | 0.5266 in | 13.375 mm |
| Tensile stress area | 0.2260 in² | 145.81 mm² |
| 5/8-18 UNF (same diameter): tap drill | 37/64" (0.5781 in) | 65% thread |
Clearance hole for 5/8
The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For 5/8 a normal fit is 21/32" (0.6562 in). Never drill the clearance part with the tap drill: the screw will not pass.
| Fit | Drill | Diameter |
|---|---|---|
| Close fit | 41/64" | 0.6406 in |
| Normal fit | 21/32" | 0.6562 in |
| Loose fit | 11/16" | 0.6875 in |
How deep to drill a blind 5/8-11 hole
| Part material | Full thread wanted | Drill depth (full diameter) | Depth to drill tip (118°) |
|---|---|---|---|
| Steel or cast iron (1 × diameter) | 0.625 in | 1.261 in (about 1-1/4″) | 1.423 in (about 1-7/16″) |
| Aluminium or brass (2 × diameter) | 1.250 in | 1.886 in (about 1-7/8″) | 2.048 in (about 2-1/16″) |
Wrench size and torque for 5/8
- Hex cap screw: 15/16 in wrench; heavy hex: 1-1/16 in
- Socket head cap screw: 1/2 in hex key
| Bolt grade | Dry | Lubricated |
|---|---|---|
| Grade 2 | 97 ft-lb | 73 ft-lb |
| Grade 5 | 150 ft-lb | 113 ft-lb |
| Grade 8 | 212 ft-lb | 159 ft-lb |
Threads easily mistaken for 5/8-11
| Thread | Diameter (in) | Diameter (mm) | Pitch |
|---|---|---|---|
| 5/8-11 UNC (this page) | 0.6250 | 15.88 | 11 TPI (2.31 mm) |
| 5/8-18 UNF | 0.6250 | 15.88 | 18 TPI (1.41 mm) |
| M16 x 2 | 0.6299 | 16.00 | 2 mm (12.7 TPI) |
| M16 x 1.5 | 0.6299 | 16.00 | 1.5 mm (16.9 TPI) |
Tips for tapping 5/8-11
- Drill in stages (for example 1/4 in, then 1/2 in, then 17/32 in) so the large bit cuts on centre.
- Most grinders sold outside North America have an M14 x 2 spindle, which needs M14 accessories; check the spindle thread before buying wheels or adapters.
- In aluminium, aim for at least 1-1/4 in of engagement (2 x diameter).
- Hex cap screws of this size take a 15/16 in wrench; heavy hex 1-1/16 in.
Frequently asked questions
What size drill bit for a 5/8-11 tap?
17/32" (0.5312 in), which gives about 79% thread. The exact 75% size is 0.5364 in (13.63 mm).
How deep should a blind 5/8-11 hole be?
For a full thread of 1 × diameter in steel, drill about 1.261 in (about 1-1/4″) at full diameter with a plug tap, or 1.423 in (about 1-7/16″) to the drill tip; in aluminium, about 1.886 in (about 1-7/8″).
What thread is an angle grinder spindle?
5/8-11 UNC on most grinders sold in North America for 4-1/2 to 5 in wheels; M14 x 2 on most grinders sold elsewhere.
What size drill for a 5/8-11 tap in mm?
13.6 mm (0.535 in) gives about 76% thread; 13.5 mm gives a slightly deeper thread, about 79%.
Sources and method
Every dimension and percentage on this page is computed from the formulas listed, not copied from another chart. Values are basic (nominal); real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric).
- ASME B1.1 and FED-STD-H28/2B (Unified inch), ISO 68-1 and ISO 261 (metric): basic thread profile and stress area formulas.
- Machinery’s Handbook (Industrial Press): percentage-of-thread relation used by our tap drill size calculator.
- ASME B94.11M twist drill series (number, letter, fractional); 0.1 mm metric drill steps.
- ISO 273 metric clearance holes; inch close, normal and loose fits as published in the ASME B18.2.8 clearance classes.
- SAE J429 and ISO 898-1 proof strengths; T = K × D × F torque relation (see our bolt torque chart for the full method).
- Wrench and hex key sizes: ASME B18.2.1, ASME B18.3, ASME B18.6.3, ISO 4014/4017, DIN 933 and ISO 4762 values as widely published.
More thread and fastener tools
- All thread and fastener charts
- UNC and UNF thread chart
- Metric thread pitch chart
- Tap drill chart (inch and metric)
- Clearance hole chart
- Nail size chart
- Wood screw size chart
- Lag screw pilot hole chart
- Bolt torque chart
- Wrench size chart
- Drill bit size chart
- Thread engagement chart
- Nail gun nail sizes by gauge
- Screw and nail size calculator
- Tap drill size calculator
- Clearance hole size calculator
- Tapped hole depth calculator
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.