Type A - composed of a top board with double hook, a holding down plate with teeth and an M10 (or M8) inner-hexagon-bolt.

Type B - composed of a top board with double hook (where one hook can draw together two neighboring steel gratings),a holding down plate with teeth and a M10(or M8) inner-hexagon-bolt.  

Type C - composed of a top board with double hook and a M10 (or M8) hexagon-bolt which can be welded in the supporting structure.