Spring
Bostitch Nailer Parts By Model Number

Price: $24.78
Found under the following brands:
Annovi Reverberi-AR, Westward, Bostitch, Black & Decker, Craftsman, Devilbiss Air Power, DeWalt, Emglo, Excell, Porter Cable, Speedaire
Pusher spring assembly w/ pin and roller. Order an extra for a spare.