Abstract: A printing apparatus including separate serial printing heads mounted on a rotary chase whereby the heads can be selectively positioned for printing on material as the material is transported through the apparatus. The chase is mounted on a support located in an easily accessible position in the apparatus whereby the rotation of the chase to change the head or heads to be used in a printing operation can be easily accomplished. The chase is also removably positioned on the support so that an entire chase can be readily separated from the apparatus, and a different chase with different printing heads substituted in the apparatus. The chase is equipped with guides which cooperate with guides on the apparatus frame to insure automatic alignment of the chase as it is located in operating position, and the drive shafts carrying the printing heads are at the same time automatically engaged with drive means associated with the apparatus.