11mm I.D. x 20mm O.D. GUHRING GuhrOJet Peripheral Coolant Fed Hydraulic Chuck Reduction Sleeve For clamping smaller shank diameter in hydraulic chucks | for tool shank tolerance h6 | concentricity deviation ? 2 um | with adjustable limit stop | with coolant slots for peripheral cooling, improving machining process and extending cutting tool life | the application of reduction sleeves permits transferable torque increase of approximately 25% in comparison to direct clamping. The reduction sleeve outside diameter must match your hydraulic chuck's nominal inside diameter. Reduction sleeves are available in 6 different outside diameters; 1/2\