We found years ago that the best system for a "ring lock" was to, instead of having a shackle attached independently to the sail and the ring, was to take the ring and a long "D" shackle to a local welding shop and have them weld the ring directly to the top of a standard (not twist) "D" shackle, then tie off the halyard to the top of the ring so that when you pull the sail up, the ring automatically seats over the "hook" (we call it a parrots beak), and when you pull the sail up and rotate the mast to release the lock, the ring always stays at the same angle to the mast as that of the sail and it releases faultlessly every time.