Xeros is a light-weight ABS plastic rockstop, 3″ square with a deep cup in the center to hold either a bare endpin tip or one with a rubber cap.  The bottom of the Xeros has rubber backing.  The webbed strap adjusts from 16″ to 29″ and has a 2″ D-shaped ring on the other end.  Place the chair leg through the ring to hold in place.