Gasket B

This is a genuine Hitachi replacement part, it is sold individually.
The purpose of the 877325 Gasket is to create a seal between the Exhaust Cover and the Main Body of the nail gun models shown below.
Because of the pressure this Gasket is subject to it will wear and will need to be replaced
Indications are an air leak, sluggish or not sinking the nail, or the driver not retracting.