Abstract: An impact printer head mechanism for printing on a print medium has a cylindrical print head with its axis perpendicular to the print line and a matrix of characters on its exterior surface in the form of a multi-turn helical row. A rotatably fixed screw thread cooperating with an internal screw thread on the print head is provided for supporting the print head for rotational and axial movement. A print head drive, including a gear cooperating with a spline on the print head, is provided for rotating the print head to simultaneously rotatably and axially move it to position a desired character relative to the print line. Operating means is provided for moving the print head relatively to the printing medium to cause a selected character to be printed.