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