in bushing 32 as shown in fig1 however as shown in fig2 when the housing 26 is pressed axially the key 28 engages one of the slots 42 in bushing 32 and consequently rotation of the housing 26 produces corresponding rotation of the bushing 32 and the bindingly engaged shaft 18 in this manner the shaft 18 is rotatably engaged only by applying sufficient axial force to the housing 26 to overcome the pressure exerted by spring 46 against washer 44 then the control device 10 may be adjusted by applying a torque to housing 26 sufficient to overcome the frictional drag exerted on shaft 18 by the shaft lock fastener 22 accordingly when the housing 26 is released the key 28 is withdrawn from slot 42 by resilient pressure of coil spring 46 against washer 44 as a result subsequent idle or accidental rotation of the housing 26 does not cause rotation of the shaft 18 to upset the adjustment of control device 10 furthermore the coil spring 46 is advantageously located externally of the housing 26 where it cannot interfere with relatively movable parts such as the walls of housing 26 and the adjacent walls of independent bushing 32 for example also by locating the spring 46 externally of housing 26 it cannot interfere with the key 28 engaging the recess means in bushing 32 when desired from the foregoing it will.