Home › Imperial Fine (UNF) › 9/16-18
9/16-18 UNF bolt size
13/16 in wrench
across-flats spanner / socket size for 9/16-18
9/16-18 UNF bolt — heavy automotive joints.
Full specification
| System | Imperial UNF |
| Nominal diameter | 9/16 in (14.29 mm) |
| Thread pitch | 18 TPI (fine) |
| Wrench / spanner (across flats) | 13/16 in |
| Tap drill | 33/64 in |
| Clearance hole | 37/64 in |
| Common grade / class | Grade 5 |
| Typical torque | 165 Nm (122 ft·lb) |
| Closest other-system size | ~9/16-12 coarse |
🔧 Torque unit converter
Pre-filled with the typical torque for 9/16-18 (Grade 5, dry). Edit any field to convert.
⚠️ Torque values here are general references for Grade 5 on clean, dry threads. Lubrication, coatings, and the joint material change the figure significantly. For structural, automotive, or safety-critical work, always use the torque specified by the manufacturer or engineer.
About 9/16-18
9/16-18 fine thread appears in heavier automotive applications.
A 13/16 in wrench is often missing from basic sets — add one for this size.
Frequently asked questions
- What size wrench or spanner fits 9/16-18?
- 9/16-18 UNF bolt uses a 13/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 9/16-18?
- A typical tightening torque for 9/16-18 UNF bolt in Grade 5 on dry threads is about 165 Nm (122 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 9/16-18 use?
- 9/16-18 UNF bolt has a thread pitch of 18 TPI (fine) and uses a 33/64 in tap drill, with a 37/64 in clearance hole.