Fuel Injection Drive Shaft O-ring. Fits MEP006A Military Generator. This seal is very specific in size and the use of one that is not identical will cause the governor to run full throttle possibly causing damage to the engine. Make sure when installing your Fuel Injection Pump that you use this specific O-Ring. Do not use one that "looks" the same size. Also used on Stanadyne Roosa Master Fuel Injection Pumps. See related items for the rest of the installation parts required.