Prox Racing Parts 28.SIS1336-2 Steel Intake Valve and Spring Kit Fits: Honda CRF 250 R 2004-2007, CRF 250 X 2004-2013 ProX Steel Valve & Spring Kits offer increased durability and less wear under extreme conditions, easily lasting 3 times longer than the OEM Titanium valves Nitrided valves offer high microhardness while super smooth surface finish reduces friction between stem and guide Spring are made from premium chrome vanadium steel for higher performance and durability under high RPM. These stronger valve springs deal with the extra weight of the steel valves Fully rebuildable with OEM retainers, bases and seals without the need of any further engine modifications