Hydraulic expansion toolholders Modern machining processes place special demands on the tool holder. Hydraulic expansion toolholders therefore offer good support combined with precise concentricity. They also enable quick and easy tool changes. Turning the pressure screw creates sufficient pressure in the pressure chamber, which leads to elastic deformation of the expansion clamping sleeve, whereby the tool is powerfully clamped - with precise concentricity. This ensures a secure and friction-locked fit. If reducing bushes that can accommodate different tool diameters are used, the tool insert can be extended as required.