Sentence:  A, is the steam or air cylinder for forcing the <WSD>dolly</WSD> B, hard against the rivet head while rivetting: when used for making rivets the <WSD>dolly</WSD> B, is unshipped, and the rivet heading apparatus substituted. 
Meaning of the word marked with <WSD> tags:  A tool with an indented head for shaping the head of a rivet.