Abstract: Spark plug insulators are mounted vertically around the edge of a horizontal turntable. A screen printing head is arranged horizontally above a print transfer drum that is rotatable about a horizontal axis. Pads of a relatively hard resilient material are disposed about the drum. The printing head is brought down into contact with the top, horizontal pad on the drum, so that the pad takes up ink, and the drum is then rotated to a vertical position. As the turntable is rotated, a pair of rollers are urged by a cam surface into contact with the insulator, rolling the insulator along the vertical print transfer pad to take up ink from the pad. The ink is ceramic-based in a thermoplastic carrier. The printing head is heated by passing current through a conductive screen so as to render the ink flowable, the print transfer pads being heated to maintain the ink flowable until it is deposited on the insulator.