The belt is toothed on {TAIL ~ one side} and not on {HEAD ~ the other side} so that some slippage can occur 
The belt is toothed on { TAIL ~ one side } and not on { HEAD ~ the other side } so that some slippage can occur
OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH