The ultimate in high-performance valves for the serious engine builder No compromise design High-flow design includes a 50 degree seat angle, no dish valve face and 5mm stem diameter (intake and exhaust) for better flow, higher compression and higher rpm Exhaust valve has a 5mm stem and is not compatible with stock retainer and lock. Will need to use retainer PART #0926-2036 and lock PART #0926-1820. Valve guide will also need to be machined to accept larger stem size.. VALVE INTAKE CRF250 ND HF