Abstract: In an impact type printing apparatus, leak of impact noise to outside can be reduced by (1) arranging the print head, platen and sheet exhaust port almost in a line and (2) setting the shape of guide ribs provided at the internal surface of cover having the aperture so that the envelope of guide ribs which has come closest to the platen at the center and periphery thereof of the sheet and is gradually separated from the platen at both ends of the sheet. Moreover, the optimum exhaust port can be selected depending on the type and thickness of sheet by rotation of cover or providing the slide mechanism.

Abstract: A knob for manually rotating a shaft provided with a flat side partially cut parallel to its axis at its end. The knob is provided with a cylinder portion having an inner hole surface which tightly fits over the end of the shaft having the flat side. The knob further is provided with a slot cut in a flat wall of the cylinder portion along its axial direction.

Abstract: A print head mounting mechanism for a printer is disclosed by which positioning of a print head in the forward and backward directions, leftward and rightward directions, and upward and downward directions with respect to a carrier can be achieved readily. The mounting mechanism includes a print head mounting plate secured in an integrated relationship to the carrier and having a predetermined thickness. The print head mounting plate has a U-shaped recess having a predetermined width and a predetermined depth. A mounting section for fitting in the U-shaped recess is provided on the print head. The print head is mounted on the carrier in an accurately positioned condition by fitting the print head mounting section into the U-shaped recess and urging the print head in the rearward direction and also in the downward direction by a wire spring.