This tool lets you set a stop, indexed to the miter slot, so you can repeatedly cut thin slices off a board for making veneers or a bent laminate. with this gauge, the offcut piece won't be trapped between the TS fence and the blade, and is more accurate since you always have the wood against the TS fence.
based on this Rockler product:
You'll need an m8 hex head bolt, nut, and washer for the knob. you might also want a bearing so you'll need a m4x10mm screw and 624 bearing.
you can print out and glue a scale to it (there's little arrows on the green part)