S size. Guaranteed you require some force, but this is due to the fact that the fast change buckle is held in place by friction. This might be the weak point to someone but I have found this being of no issues for me, the sling hasn't missed a beat, https://barska-compact-biometric85295.uzblog.net/the-definitive-guide-to-bulldog-belt-slide-holster-blk-48397350