Normally, {TAIL ~ the envelope} will not contact {HEAD ~ either guide rail} 17 or guide rail 18 
Normally , { TAIL ~ the envelope } will not contact { HEAD ~ either guide rail } 17 or guide rail 18
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH