Small enough to fit in a camera zoom lens and other precision motion applications, these carriages and guide rails have a black chrome-plated finish that diffuses light to prevent reflecting light from causing equipment to malfunction. They are also useful in positioning systems that use photosensors, which are sensitive to light. The finish gives you two times more rust resistance than 440 stainless steel alone. The carriage comes already installed on the guide rail. However, the ball bearings don’t have a cage, so they’ll fall out if you remove the carriage from the guide rail. Mount them in any orientation without affecting load capacity.