9/16″-18 UNF Thread
Recommended tap drill 33/64″
Tap drill Ø 0.5156″ / 13.097 mm
Major Ø 0.5625″ / 14.287 mm
Threads per inch 18
The chart recommendation gives approximately 65% thread engagement — the conventional target for average materials. It is not the only valid choice; see the options below.
Specification
| Designation | 9/16″-18 UNF |
|---|---|
| Thread family | Unified National Fine (UNF) |
| Nominal size | 9/16 |
| Basic major diameter | 0.5625″ / 14.287 mm |
| Threads per inch / pitch | 18 TPI (1.411 mm pitch) |
| Recommended tap drill | 33/64″ (0.5156″ / 13.097 mm) |
Tap drill options by thread engagement
Any of these standard drills produces a usable engagement for 9/16″-18 UNF; smaller drills give stronger threads but higher tapping torque. Percentages use the conventional approximation (60° thread form).
| Drill | Decimal in | mm | Approx. engagement |
|---|---|---|---|
| 12.8 mm | 0.5039 | 12.8 | 81.1% |
| 12.9 mm | 0.5079 | 12.9 | 75.7% |
| 13 mm | 0.5118 | 13 | 70.2% |
| 33/64″ — chart recommendation | 0.5156 | 13.097 | 65% |
Nearest drills to the tap drill in other systems
| Drill | Size | vs 33/64″ | Resulting engagement |
|---|---|---|---|
| 13 mm | 0.5118″ / 13 mm | −0.097 mm | 70.2% |
Hex bolt & nut dimensions
For a standard hex cap screw (ASME B18.2.1) and finished hex nut (ASME B18.2.2) in this size.
| Wrench / socket size (bolt head) | 13/16″ |
|---|---|
| Wrench / socket size (nut) | 7/8″ |
| Head height | 23/64″ (0.3594″) |
| Nut thickness | 31/64″ (0.4844″) |
| Compatible nut | 9/16-18 hex nut |
Basic (nominal) dimensions. See the wrench & socket size charts for all sizes and the metric ↔ SAE socket comparison.
Related threads
- 9/16″-12 UNC — same nominal size, 12 TPI (Unified National Coarse (UNC)) · compare
- 1/2″-20 UNF — next size down in UNF
- 5/8″-18 UNF — next size up in UNF