This is an improved centering Jig for Lacroix Boards prototipo board's wheel pulley. a 62T pulley attached to MBS rockstar II hubs.
the original was just a spacer. This one is is a wedge deigned to screw onto the axel and wedge itself into the pulley thereby centering it.
To use, flip your wheel onto to your axel backward. the pulley bolts should be loose. screw the jig onto the axel so it wedges itself into the wheel pulley. then tighten up the pulley bolts. remove the jig. reinstall the wheel as normal. see picture.