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