Abstract: A printing mechanism requires ribbon spools to be locked in place radially, and includes a pivoting ribbon tension arm that must be pivoted out of its normal operating position when ribbon is to be replaced. A ribbon spool lock assembly includes a rotating locking hub on the side of the printing mechanism. The rotating locking hub includes a locking feature that protrudes into the printing mechanism to radially lock the ribbon spool when the locking hub is in a locked position. A pivoting lock arm is provided for pivoting the locking hub into an unlocked position in which the locking feature is disengaged from the ribbon spool.