Abstract: A lock construction including an outer case having a central opening that receives a cylinder. A plurality of plate-type tumblers are mounted for sliding movement within a passage in the cylinder and the tumblers have aligned slots to receive a key. The side wall of the case is provided with a longitudinal opening or window and a pair of shoulders border opposite sides of the opening. A cover encloses the opening and has a pair of side flanges that removably engage the shoulders of the case. In assembling the lock, the tumblers are inserted into the cylinder through the opening in the case and the cylinder is then rotated to effect engagement of the tumblers with the ward in the case, which is spaced 90.degree. from the opening, and the cover is then snap-fitted onto the case. By removal of the cover, the tumblers can be readily removed from the cylinder.