Pursuant to the invention, {HEAD ~ adapter blocks} can be provided having {TAIL ~ a length dimension} equal to the distance between hub axes of two connector elements joined by a rod element of a selected length 
provided having
Pursuant to the invention , { HEAD ~ adapter blocks } can be provided having { TAIL ~ a length dimension } equal to the distance between hub axes of two connector elements joined by a rod element of a selected length
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH