Rapid-Lock System adds unique safety-stop features. The feature is comprised of a 5mm diameter steel pin that engages 5.5mm diameter holes in the rail. In addition to supplementing the traditional friction-based clamping mechanism, the interface prevents unintentional repositioning of the rail within the clamp when the Rapid-Lock is engaged.
A big clamp is for Arca standard plate. A small clamp is for the gun rail.