546,711. Cylinder locks. YALE & TOWNE MANUFACTURING CO. Sept. 17, 1940, No. 14302. Convention date, Oct. 14, 1939. [Class 44] To prevent picking a cylinder lock a series of wafer discs 17 is disposed between each tumbler 16 and its driver 19 so that any key which can enter the keyhole in barrel 11 can effect release of the barrel and limit rotation thereof, rotation being arrested by a stop device which is automatically released to allow further rotation if the correct key is being used. In the arrested position the tumblers are out of line with the drivers and cannot be manipulated to effect improper release. In the locking position, Fig. 1, the springs 23 hold the inner ends of the drivers just within the apertures in the barrel 11 to lock it. Any key may be used to register the dividing surface between one or other pair of adjacent discs with the surface of the barrel to release it: The correct key, however, also brings staggered grooves 20 provided in the drivers into alignment in register with a blade member 21. Blade 21 is carried by a slider 29 housed in a bore 33 in casing 10 and urged towards the front end of the casing by a spring 37, and its edge has segmental notches 40 which, in the normal or locked position, embrace the drivers so as to allow their free operation. The blade is held in the normal position, against the action of spring 37, by an arm 45 carried by member 29 and resting on a cam hump 44 formed on one wall of an annular groove 42 in an extension at the rear end of the barrel. The other wall of this groove opposite hump 44 is cut away to provide stops 43 which co-operate with arm 45 to limit rotation of the barrel. When the barrel is released and rotated, hump 44 moves away from arm 45, but member 29 is held against sliding movement by the drivers 19 co-operating with the notches 40, so that arm 45 remains in the path of the stops 43 as in Fig. 7, unless grooves 20 have been aligned in register with blade 21 by use of a correct key. In this case, the unnotched portidhs 41 of the blade edge can enter grooves 20, so that member 29 is slid by spring 37 to move arm 45 away from stop 43 and into register with groove 42 so that rotation of the barrel may be completed. Fig. 8 shows a modification in which a radially slidable block 53 at the rear end of the casing rests in a groove 60 at the rear end of the barrel 11, to limit its rotation. The block is held against outward movement by the inner tapered end of a slide 50 urged rearwards by a light spring 52. Slide 50 has lateral lugs cooperating with the drivers in a manner similar to that of the unnotched portions 41 of blade 21 described above. Block 53 carries a plunger 56 held in contact with a cam surface 59 by spring 57. When the barrel is released and rotated, block 53 is held against movement by end 62 of slide 50, plunger 56 being moved by cam 59 to compress spring 57, and block 53 co-operates with the end of groove 60 to limit rotation of the barrel, unless grooves 20 have been correctly positioned by the use of a correct key, in which case slide 50 is freed, and is moved to the right by the cam action of the block 53 on end 62, the block being moved outwards by spring 57, so that it clears groove 60 to allow completion of the barrel movement.