Sentence:  The collar is placed over the fastener <WSD>pintail</WSD> and the installation tool is placed over the pintail. The tool pulls on the pin drawing the parts together until the collar is swaged into locking grooves. 
Meaning of the word marked with <WSD> tags:  The end of a fastening pin or mandrel on a Huckbolt or pop rivet that is broken off when installation is complete.