In use, the blocks may be stacked to provide an interlocking structure wherein the protrusions of one block interfit within {HEAD ~ the insets} of {TAIL ~ another block} 
In use , the blocks may be stacked to provide an interlocking structure wherein the protrusions of one block interfit within { HEAD ~ the insets } of { TAIL ~ another block }
OTH OTH OTH OTH OTH OTH OTH OTH 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