This is a rubber primer bulb with a plastic adapter attachment that is used on a variety of lawn and garden equipment models. This bulb attaches to the carburetor and is used to pump gasoline from the fuel tank into the gas chamber of the carburetor. Over time and through regular use, the primer bulb will lose its elasticity and may crack...Read more, requiring it to be replaced. To replace your primer bulb, you simply need to locate the bulb on your machine, unscrew the housing and remove the bulb, and secure the new one. This bulb is sold as an individual part and has a 2.25cm (7/8-inch) outer-diameter and a 3.33cm (1.3125-inch) height.