Sentence:  "In Fig. i is shown one of the <WSD>chasers</WSD> in the position which it occupies in cutting a thread." 
Meaning of the word marked with <WSD> tags:  A tool used for cleaning out screw threads, either as an integral part of a tap or die to remove waste material produced by the cutting tool, or as a separate tool to repair damaged threads. (from 19th c.)