MacMedia;
The switch you are wanting to know is the Brush Wear Switch and the piston is an insulator. P/N Brush wear sw. is 29262-41H10. If I may, I would recommend that you also replace the insulator. Otherwise you will very likely see a brush fault in the PO's display. The P/N for the insulator is 26264-41H10. The other switch that's mounted on the motor is a Thermo switch and the P/N for it is 29260-41H10.
Best to You;