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7/8-inch bolt size
1-5/16 in wrench
across-flats spanner / socket size for 7/8 in
7/8-inch bolt — heavy structural steel.
Full specification
| System | Imperial UNC |
| Nominal diameter | 7/8 in (22.23 mm) |
| Thread pitch | 9 TPI |
| Wrench / spanner (across flats) | 1-5/16 in |
| Tap drill | 49/64 in |
| Clearance hole | 57/64 in |
| Common grade / class | Grade 5 |
| Typical torque | 569 Nm (420 ft·lb) |
| Closest other-system size | ~M22 |
🔧 Torque unit converter
Pre-filled with the typical torque for 7/8 in (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 7/8 in
7/8-9 is a heavy structural size used in large steel connections.
Tension this size with impact or hydraulic tools, not by hand.
Frequently asked questions
- What size wrench or spanner fits 7/8 in?
- 7/8-inch bolt uses a 1-5/16 in wrench or spanner, measured across the flats of the hex head.
- What is the torque for 7/8 in?
- A typical tightening torque for 7/8-inch bolt in Grade 5 on dry threads is about 569 Nm (420 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does 7/8 in use?
- 7/8-inch bolt has a thread pitch of 9 TPI and uses a 49/64 in tap drill, with a 57/64 in clearance hole.