feed screws or threaded rods 10 until the measuring heads 1 and 1 39 are positioned in the center area of the measuring range of the sizing device where the contacts 3 39 and 3 of the heads 1 39 and 1 are received in the slot 15 in the blade 14 and contact the grinding wheel 2 and regulating wheel 4 respectively and are then held in position by fastening the clamp 7 a clearance is defined between the grinding wheel 2 and regulating wheel 4 corresponding to a desired finish size of workpieces and the grinding wheel 2 and regulating wheel 4 are rotated as the grinding wheel 2 and regulating wheel 4 are rotated the workpiece w supported at the upper end of the blade 14 is subjected to a feed component from the regulating wheel 4 to be abutted against the grinding wheel 2 to be continuously ground thereby the ground workpieces w are transferred onto the conveyor belts 13 13 39 on the exit side of the wheels 2 and 4 to be discharged out of the machine although the present invention has been described as being applied to a centerless through feed grinding operation for a constant size the invention is equally applied to other grinding operations as those performed by centerless plunge grinding machines and double disc surface grinding machines for example according to the present invention since the distance between the grinding wheel 2 and regulating wheel 4 is measured and the distance is varied so as to correspond to different diameters of workpieces to be ground by the centerless grinding machine the grinding machine can be applied to the plunge grinding of small diameter workpieces on the other hand in the centerless.