by bow 139 during roation of key 72 when tip 76 is engaged in recess 114 of pinion gear 110 could cause shaft 136 to be severed from bow 139 to prevent that shaft 136 is mounted to bow 139 so as to rotate rather than break off when a predetermined torque is exceeded shaft 136 is attached to cylindrical plug 160 by welding for example or shaft 136 and plug 160 are formed as one piece plug 160 is in turn mounted in cylindrical recess 162 in bow 139 set screw 164 locks plug 160 in recess 162 and prevents it from rotating upon the application of up to a predetermined torque determined by the sizes of shaft 136 plug 160 and set screw 164 when that predetermined torque is exceeded set screw 164 permits plug 160 to rotate in recess 162 as mentioned above tip 76 of change key 72 may be specially configured to improve security fig2 illustrates the presently preferred y shape and fig2 illustrates a semi cylindrical shape fig2 24 illustrate removal of lock 70 from lock assembly 71 and disassembly of lock 70 screws 176 are loosened in conventional manner to remove lock 70 from lock assembly 71 pin 178 in the rear of lock 70 is pushed to release knurled nut 180 which is then.