Abstract: The combination lock is one wherein movable members of the combination mechanism are set in decoding position by a key in the form of a rotatable shaft with a head at one end serving as a handle. Rotation of the key to proper decoding position is determined by shifting an index mark on the key relative to selected units of a set of letters or numerals on the lock housing. The combination mechanism makes use of a multiple number of pairs of discs concealed in the housing which must be successively set in proper decoding position, one disc relative to the other, to release a lock operating plug. In proper decoding position a slide bar, which normally blocks rotation of the lock operating plug, is shifted by key action into openings provided in the discs and out of blocking engagement with the plug, in which position the plug is free for rotation by the key.