Formed to fit the closed end of canister style oil filters for easy removal and installation of the filter. Fits to the end of a standard 3/8" socket wrench or wrench extension. For us on 4-stroke outboards (see specific models below) or other engines with screw on type oil filters. Produced by Mercury Marine to our stringent original equipment manufacturer specifications to maximize the performance of your Mercury and Mariner outboard or MerCruiser stern drive