disclosed is an improved serial impact printer which both prints and serrates a document . the printer includes a print wheel which is rotated to position a selected character in front of an anvil . the print wheel includes a wheel - like circular member having print characters at the end of fingers which extend from the top of the print wheel &# 39 ; s perimeter . an impact mechanism pressures the selected print character against the anvil , the document being positioned between the selected print character and impact mechanism . the impact mechanism includes a d . c . motor which turns a threaded shaft which is engaged with a threaded hole in the end of a hammer . counterclockwise motion of the d . c . motor advances the hammer &# 39 ; s head to pressure the back of the print character against the anvil , thereby printing and serrating the document with the selected character . thereafter , clockwise motion of the d . c . motor restores the impact mechanism to its original position .