Outer diameter 26.5mm Diameter for piston bore in the fork: 19.5mm Total height of the valve: 14mm YSS fork valves give a conventional fork a controlled feel with improved road contact. CAD designed and hardened from extremely lightweight 6061 T6 aluminum with 65 Rockwell. Finely adjustable and suitable for almost all fork diameters. Through a sophisticated system of holes in the valve, the oil flow in the fork is changed so that the road contact and the feedback is much more direct. The driver gains thereby safety and feeling for the road surface. Application: On-, offroad, racing- and touring applications. The fork valves come ready set for the respective fork diameter. A subsequent fine adjustment can be done by the amount of oil or other oil viscosity. Operating principle: The YSS fork valve is used between the piston rod and the fork spring. For this it is important to know in advance the inside diameter of the dip tube and the bore in the piston rod. Depending on the fork valve diameter used, additional oil flow holes must be drilled in the piston rod. This is described in detail in the installation instructions. The fine tuning of the fork valve is possible after installation with little effort: The fork bridge has to be loosened, the oil has to be pulled out of the fork and the fork valve has to be lifted upwards. Then use an Allen key to tighten or loosen the set screw in 2-turn increments. Please remember to first turn the upper screw and then tighten with the lower stop nut.