As can be seen in FIG 3, alignment hole 16 is in {HEAD ~ the shape} of {TAIL ~ a comer} cut out 
As can be seen in FIG 3 , alignment hole 16 is in { HEAD ~ the shape } of { TAIL ~ a comer } cut out
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH