The adjustment knob on the wheel stop chock is plastic fastened to a 1/2 inch steel threaded shaft with a steel spring pin. After repeated use the plastic knob cracks and breaks (go figure). This can be fixed using a steel threaded 1/2 to 3/4 inch adapter, drilling the center to fit the 1/2 inch steel shaft, drilling another hole in the side of the piece to fit the steel spring pin and fastening it to the shaft using the manufactured hole. Adjust the chock using a combination wrench or ratchet. BAL makes an all steel X-chock but its extra price is worth the quality improvement and you won't be left out in the woods with a broken chock.