A radial force device for a contour measuring instrument for measuring a contour of a shaft-shaped workpiece which can be rotated about an axis of rotation. The radial force device has a clamping body, a force introduction roller, at least one counter-roller and a coupling device. The clamping body is shaped for fitting radially around a workpiece portion, received in the contour measuring instrument, of the workpiece. The force introduction roller is designed to apply a mechanical radial force to the workpiece in order to apply a load to the workpiece, wherein the force introduction roller is mounted in a radially movable manner on the clamping body. The counter-roller is mounted in the clamping body and designed to support the workpiece during the application of the force. The coupling device is shaped for coupling the clamping body to the contour measuring instrument.