To fasten tighter, there's serration beneath the head. It's usually put on office chair system, wooden furniture, and steel furniture. The range of such model is comprehensive.
1. M5-0.8; length: 10mm ~ 80mm.
2. M6-1.0; length: 10mm ~ 80mm.
3. M8-1.25; length: 12mm ~ 90mm.
4. M10-1.5; length: 16mm ~ 100mm.
5. Inch size also available.