Abstract: Centerless honing machines are described for honing external cylindrical surfaces on a series of workpieces. Each machine comprises a pair of spaced adjacent rotary rollers for supporting and rotating workpieces while also causing them to travel axially along the rollers, at least one honing stone for engaging and honing the workpieces, a fluid pressure operated device for pressing the honing stone against the workpieces, a gaging device for gaging the size of the workpieces and for producing gaging signals, a pressure regulator for supplying fluid pressure to the fluid pressure operated device, and control means operable in response to the gaging signals for adjusting the pressure regulator to increase or decrease the fluid pressure and thereby to increase or decrease the amount of stock removed from the workpieces by the honing stone to achieve closer agreement between the finished size of the workpieces and the desired size.