Mounting apparatus is used for supporting an accessory device, e.g., a sensor, in a manner permitting adjustment. An accessory device-receiving mount is fixable to the accessory device and has at least one surface forming a cross-section permitting adjustment in at least one degree of freedom. A clamp ring engages the device-receiving mount at the surface, so that the cross-section permitting adjustment. A clamping mechanism selectively clamps the clamp ring and includes a manually threaded fastener and a lever-operated clamp tightener. The lever-operated clamp tightener acts on the manually threaded fastener to releasably tighten the clamping mechanism beyond that achieved by manually threading the manually threaded fastener, permitting manually threading the clamping arrangement at a maximum tension less than a full tension applied by the lever-operated clamp tightener.