Jims Manual Compression Release Valves Features: Give your starter a hand by installing these in your high-compression, big-inch motor These need to be installed by an experienced mechanic/machinist Can be installed in all Big Twin, XL and Buell motors Fits dual-plug heads or heads that have been machined for dual plugs Requires a 10mm x 1.0mm drilled and tapped hole in your cylinder head for use Made in the USA