Ordering by number: this is 470W740293, the Chicago Pneumatic O-Ring. It seals a pressure joint inside the tool, and because elastomer takes a set long before the metal around it wears, it is one of the first items to replace when a machine starts weeping air or oil.

If you are working from a machine rather than a part number, start at the full diagram library, or send us the model and serial and we will match it. Machines themselves are on the CP tool catalog. Denver stock, with same-day shipment on in-stock orders in by 4 PM ET.

• Part number: 470W740293
• Manufacturer: Chicago Pneumatic
• Crowder SKU: CP-470W740293