Abstract: In a printer adapted to receive any of a plurality of petal-type printing thimbles, each of the printing thimbles is provided with a recognition code-forming portion containing a plurality of protuberance-forming positions, the arrangement of protuberances at the protuberance-forming positions defining a thimble recognition code which identifies specific character position, hammer impression, and character spacing tables. These tables identify the character positions, hammer impression forces and character spacings required to print characters designated by character codes when the recognition code identified printing thimble is mounted on the printer. A mechanical means, mounted on the printing hammer cover of the printer carrier unit, detects the presence or absence of protuberances at the protuberance-forming positions of the code forming portion on the printing thimble, to generate a binary recognition code received by the printer processor.