This is a 2 Bar Slide designed for use with 3" webbing. Its sole use is to thightly wrap a 3" shoulder belt around a bar or pin. It is lighter than a 3 Bar Slide and offers virtually no slip when wrapped correctly. Even a correctly wrapped 3 Bar Slide will has what is called microslip - when a small amount of webbing slips through the bracket when a significant load is placed on the webbing.
While this 2 Bar Slide is safer, it is much harder to wrap in if you are not used to doing it. Once you figure out the trick, it's not hard at all.