When combined with IronRidge UFO Clamp it performs the same function as an "End Clamp" does for other rail systems
 
The IronRidge Stopper Sleeve snaps onto the IronRidge UFO to transform it into an end clamp. It comes in clear and black finishes and 8 different sizes to accommodate a range of module frames.
 
(we may not have all finishes available for sizes, but we keep all sizes stocked)