The CMI cable gage is a precision device for measuring cable wear. Sized to fit 1/2" , 3/8" and 1/4" cables. Features a hole on one end for attaching to harness via a small piece of accessory cord and anodized bright red for visibility. New cables will not fit into the grooves. Once a cable has worn down 5%, the cable will slip into the groove indicating the need to replace it. CMI highly recommends that cable wear be checked on a regular basis to ensure the safety of zipline users.