The carriages are driven by either a trapped or internal inear belt that can be adjusted to reduce lash is driven along the external roller bearings These units are ideal for applications in clean rooms with a clean-room classifications of 1.000 (corresponding to US Fed. Standard 209 E). This arrangement allow for easy adjustment and belt tensioning, which can be readjusted by a single screw adjustment device in the carriage. The pulleys have maintenance-free ball bearings.