The anchor is {HEAD ~ an elongate cylindrical shell} with {TAIL ~ a central passage} to receive the bolt, thereby forming an anchor bolt unit 
with
The anchor is { HEAD ~ an elongate cylindrical shell } with { TAIL ~ a central passage } to receive the bolt , thereby forming an anchor bolt unit
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH