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3/8-24 UNF bolt size
9/16 in wrench
across-flats spanner / socket size for 3/8-24
3/8-24 UNF bolt — automotive and machinery.
Full specification
| System | Imperial UNF |
| Nominal diameter | 3/8 in (9.53 mm) |
| Thread pitch | 24 TPI (fine) |
| Wrench / spanner (across flats) | 9/16 in |
| Tap drill | Q (8.4 mm) |
| Clearance hole | 25/64 in |
| Common grade / class | Grade 5 |
| Typical torque | 53 Nm (39 ft·lb) |
| Closest other-system size | ~3/8-16 coarse |
🔧 Torque unit converter
Pre-filled with the typical torque for 3/8-24 (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 3/8-24
3/8-24 fine thread is used in automotive and machine adjustment.
Tag fine-thread bolts — mixing them with coarse 3/8-16 ruins both.
Frequently asked questions
- What size wrench or spanner fits 3/8-24?
- 3/8-24 UNF bolt uses a 9/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 3/8-24?
- A typical tightening torque for 3/8-24 UNF bolt in Grade 5 on dry threads is about 53 Nm (39 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 3/8-24 use?
- 3/8-24 UNF bolt has a thread pitch of 24 TPI (fine) and uses a Q (8.4 mm) tap drill, with a 25/64 in clearance hole.