This is a high-quality manufacturer-sourced part which is made for use with Campbell Hausfeld nailers. The head valve is located on the back of the nail gun, in the top exhaust port. Over time components may wear out and begin to fail eventually requiring replacements. For the proper application please refer to the appropriate diagrams of your model. This kit includes the o-rings, the piston bumper, the head valve, and the spring. You will need a screwdriver and a wrench set to remove the top cap and perform the repair.