The knob 80 has an annular portion 82 arranged for frictional engagement with {TAIL ~ the exterior surfaces} of the rear wall 66 on {HEAD ~ each side} of the slot 76 
The knob 80 has an annular portion 82 arranged for frictional engagement with { TAIL ~ the exterior surfaces } of the rear wall 66 on { HEAD ~ each side } of the slot 76
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH