Home › Set / Grub Screws › M8 grub
M8 set screw size
4 mm hex key
Allen / internal hex key size for M8 grub
M8 set screw — heavy couplings and collars.
Full specification
| System | Metric (45H) |
| Nominal diameter | 8 mm |
| Thread pitch | 1.25 mm |
| Hex key (Allen) | 4 mm |
| Tap drill | 6.8 mm |
| Clearance hole | n/a (threaded) |
| Common grade / class | 45H |
| Typical torque | 14 Nm (10.3 ft·lb) |
| Closest other-system size | ~5/16 inch |
🔧 Torque unit converter
Pre-filled with the typical torque for M8 grub (45H, dry). Edit any field to convert.
⚠️ Torque values here are general references for 45H 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 M8 grub
M8 grub screws hold heavier couplings and collars on larger shafts.
A 4 mm hex key drives M8 grubs — use a ball-end key for tight clearances.
Frequently asked questions
- What size Allen / hex key fits M8 grub?
- M8 set screw uses a 4 mm hex (Allen) key with an internal hex drive.
- What is the torque for M8 grub?
- A typical tightening torque for M8 set screw in 45H on dry threads is about 14 Nm (10.3 ft·lb). Always confirm against the manufacturer spec for important joints.
- What thread pitch and tap drill does M8 grub use?
- M8 set screw has a thread pitch of 1.25 mm and uses a 6.8 mm tap drill, with a n/a (threaded) clearance hole.