The frame may be rectangular, when each side comprises {HEAD ~ at least one projection}, {TAIL ~ typically a lug}, or at least one longitudinal array of loops 
The frame may be rectangular , when each side comprises { HEAD ~ at least one projection } , { TAIL ~ typically a lug } , or at least one longitudinal array of loops
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH