With the seats and springs back in place put some plumbers grease on the large O ring on the cartridge then push the cartridge into place. note the grove in the body, the cartridge can only go in one way, Now put plumbers grease on the threads on the shower body, so that the next time the nut needs to be removed, it will come off easy. Adjust the set screw as the old one was or as you want it. If you have small children, adjust it so that the water will not be higher then 120 degrees F Put the handle and button back on, turn the faucet you have on, off and turn the water on slowly. You are done.