keyway 15 through a circular port 22 in the front face of box 12 thus the front edge of keyway 15 is recessed that is spaced slightly from the front face of box 12 a rotatable shaft 23 is supported from the inside of the back plate of box 12 and extends through the front face thereof to carry or operate the components of an actuation assembly indicated generally by the numeral 24 a handle 25 is mounted on shaft 23 exteriorly of box 12 to permit facile rotation of the shaft mounted on shaft 23 interiorly of box 12 is a cam plate 26 which rides against a rearwardly extending flange 27 of a keyway blocking plate 28 blocking plate 28 is slidable horizontally in the space defined vertically by flange ends 20 and 21 of mounting plate 19 and on the sides by the front face of box 12 and the front edge of keyway 15 thus blocking plate 28 is normally positioned between port 22 in box 12 and keyway 15 and is slidable therebetween blocking plate 28 has a slot 29 therein so that when the locking mechanism is locked as shown in fig2 access to keyway 15 may be had therethrough a coil spring 30 is mounted between a clip 31 formed in blocking plate 28 and a clip 32 formed in mounting plate 19 to maintain cam plate 26 in contact with flange 27 a clockwise rotation of shaft 23 by the external handle 25 moves blocking plate 28 to the left from.