Abstract: Chain or belt printers for high speed print-out from computers and the like employ metal or plastic type slugs clipped to a toothed elastomeric timing belt. The belt passes around two toothed pulleys one of which drives the belt so that the type slugs pass along a printing line at a predetermined speed. Pins holding and locating the slugs on the belt extend inside both top and bottom edges of the belt.The pulleys are constructed with peripheral slots to mate with the teeth on the inner surface of the timing belt and added teeth to support the belt at both of its outer edges and between the pins holding the slugs to the belt. This added support for the belt improves the printing accuracy under dynamic high speed printing operations.