Abstract: The invention relates to a tool-holder for machine tools, particularly boring machines, of the type having a cylindrical body which is traversed by a slot shaped whereby that part of the body which supports the tool is displaceable resiliently relative to the remaining part of the body in a direction perpendicular to the axis of the body. Hydraulic means are provided for effecting the transverse displacement of the tool support part to adjust the position of the tool in a radial direction. According to the invention, these hydraulic means are arranged to exert a substantially uniform pressure to the outer surface of the body of the tool-holder.