Ordering by number: this is 4700W65102, the Chicago Pneumatic O-Ring. Its job is to hold the pressure boundary between two mating faces; a hardened or nicked seal shows up as lost power and a damp housing well before anything else fails.

Give us the model and serial off your machine and we will confirm the fit; the parts diagram library and the CP tool catalog are the other two places to start. It ships out of Denver, same day on in-stock orders placed before 4 PM ET.

• Part number: 4700W65102
• Manufacturer: Chicago Pneumatic
• Crowder SKU: CP-4700W65102