Both the seating rim and the seating recess can be of {HEAD ~ a polygonal shape}, with the seating rim fitting the shape of {TAIL ~ the seating recess} of the sample changer 
Both the seating rim and the seating recess can be of { HEAD ~ a polygonal shape } , with the seating rim fitting the shape of { TAIL ~ the seating recess } of the sample changer
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH