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