The end of the Benelli lifter has a semi circular void at the tip. When weak hand loading a shotgun rapidly your thumb can get stuck in that void. Once stuck the only way to remove the thumb is to yank it out which usually takes the thumb nail with it. The lifter gets weled up by filling in the void and extending the length a bit. The lifter then needs to be tuned so the extra length doesn't cause the shells to feed into the top of the receiver.