A rotary milling head for boiler tube stub removal with cylindrical cutting pieces removably secured to the milling head by forces exerted by the material being cut and by friction, without any separate securing element. A relay control unit 12 normally brings a relay 11 in a state in which its input terminal is connected to an A terminal 13. The resulting nickel cap may be wire-bonded directly, without the deposition of a gold cap layer. The detection end is coupled to one of the sense electrodes and configured to acquire a predetermined number of sampled values corresponding to the cycle data associated with the coupled sense electrode and generate a response signal to the drive end according to the sampled values, wherein the drive end resends the cycle data according to the response signal.