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