OBP 0.700" bore, (17.78mm) master cylinder repair/rebuild kit. All master cylinders can wear over time, they are designed so that the softer rubber seals wear rather than the harder aluminium bore. There are exceptions to this inherent design principle, for example water can cause corrosion, push rods running at extreme angles can cause some ovality and if dust and dirt finds it's way into the system this too can cause scouring of the bore and in these extreme cases these repair kits might not provide the solution. If however you always use top quality fluid, change it regularly and ensure proper component setup from the outset, you should find the cylinder bore remains in very good shape and the unit can successfully be overhauled and used again and again. These kits fit OBPs integral and non-integral master cylinders and come with all the necessary seals, piston, spring adn rod. Care should be taken during the process, seek help of a qualified motor engineer if required.