Hydraulic chucks

A chuck comprising a main body defining a hydraulic fluid receiving enclosure and comprising a tool receiving portion with at least one deformable wall portion, the hydraulic fluid receiving closure and tool receiving portion being arranged so that pressure applied to fluid in the enclosure can cause deformation of the deformable wall portion for gripping an inserted tool, the chuck further comprising a moveable piston which is disposed partly within the hydraulic receiving enclosure and which is moveable between a first and a second position wherein the volume displaced within the enclosure by the moveable member when the piston is in the first position is less than the volume displaced within the enclosure by the moveable piston is in the second position; and a centrifugal pressure intensifier for increasing the pressure in carried hydraulic fluid in despondence on the speed of rotation of the chuck, said centrifugal pressure intensifier being arranged to act on the moveable piston, the moveable piston comp