1. Type A composed of a top board with double hooks, a holding down
plate with teeth and a M8 inner-hexagon-bolt. 2. Type B composed of a top board with double hooks (one of hooks
can draw together the two neighboring steel gratings),and a holding
down plate with teeth and a M8 inner-hexagon-bolt. 3. Type C composed of a top board with double hooks and a M8
hexagon-bolt which can be welded in the supporting structure. |