The Enlightenment, 1700– Photos of padlocks with screw mechanisms Padlock with hinged, notched shackle and a lock body with an oval cross-section. On three sides, the lock has narrow lengthwise reinforcement bands. The keyhole is on the same short end as the joint of the shackle, and the key has internal threading. To unlock, the key – aided by a nut – withdraws the threaded bolt from the notch in the shackle so that it can be removed. Photo of a padlock with separate shackle Square iron padlock with separate shackle and turn-key locks, evolved from the corresponding lock type of the 16th century.