594,690. Locks. TRIGGS, W. W. (Yale & Towne Manufacturing Co.). June 20, 1945, No. 15770. [Class 44] A lock, for use with a key plug preferably rotatable to a release position by inserting the correct key, has a number of tumblers and a number of tumbler-controlled members or fences mounted to move relatively to the tumblers, so that a particular alignment of the tumblers will release a fence for movement, but will also prevent at least one fence from moving to release position. A series of tumblers 12 is mounted in a cylinder 10 which houses the key plug 11, and which is divided by walls 13 into compartments 14, two tumblers sliding in each compartment and interfitting and co-operating with separate springs 15, 16, which are held in position by a sliding plate 10a which closes the upper ends of the compartments. Initially each tumbler 12 rests on the portion 17 of the key plug ; when the blade 18 of a key K is inserted in the keyway 19 and rotated through a right angle, the tumblers 12 are positioned by the bitted portions 20 of the key. A number of fences 21, 22 coact with the tumblers 12 and slide in openings 23 in the cylinder 10 transversely to the tumblers. Springs 24, preferably one for each fence, project the fences inwards, when the latter are released by a particular alignment of the tumblers, towards a detent 25 mounted to slide parallel to the tumblers and having a series of ratchet-like slots 26, into any one of which the end 27 of any one of the fences may enter. This detent is preferably predisposed towards blocking the operation of the lock after some preliminary movement of the lock mechanism, e.g. the partial rotation of the key plug, but can be held back by any one fence. Each tumbler has a number of gatings 28, and each fence has a series of lugs 29 ; the key K sets the tumblers so that each tumbler has a gating 28 in alignment with the lugs 29 of a single fence, which then moves towards the detent 25 under pressure of the spring 24. Preferably there is one fence for each master key. The detent 25 is held in its upward release position by a roller 33 at the base of the detent lying against a cam 36 on the plug ; as the plug rotates, the cam 36 continues to hold the detent 25 released against the pressure of its spring 32 until the cam surface 37 moves opposite the roller 33 when the detent will be lowered, bringing one of two lugs 30 on the detent opposite one of two shoulders 31 on the plug 11 to block further rotation of the key plug. If during this rotation of the key plug a proper key K has been used, Fig. 7, a fence 21 will be released and spring-urged into one of the slots 26 in the detent 25 ; thus when the cam surface 37 releases the detent for downward movement, the end 27 of the fence 21 will hold the detent, so that the lug 30 is prevented from engaging the shoulder 31, and further rotation of the plug is possible. To release each fence a different alignment of the tumblers, is preferably required, so that in picking the lock if one fence moves into the wrong fence and gating relationship with a tumbler, that tumbler is held against movement to correct alignment. Between the slots 26, the detent has flat holding surfaces 40 which coact with flat end surfaces of the fences under pressure of the springs 2 to hold the fences against movement. Thus when the plug is in its initial position, the fence lugs 29 will not bear against the tumblers 12 which can therefore move freely when being set by the key. Picking, which cannot take place unless the fences bear against the tumblers is hindered by this arrangement since it is impossible to apply the fence lugs 29 against the tumblers 12 until the detent 25 has been partially released to withdraw its surfaces 40 from the surfaces 41 of the fences. The alignment of the tumblers to release one fence preferably positions solid portions of at least one tumbler opposite at least one fence lug of each other fence, thus blocking the release of any other fence.