This is a safety cover - vacuum cleaner adapter for an angle grinder with main hole diameter of 40mm.

Printed with white ABS 0.6mm nozzle and 0.4mm layer height. Main part printed with supports.

Assembly is straight forward, but in case you need in depth instructions, they can be found here: https://daumemo.com/diy-3d-printed-vacuum-dust-cover-for-your-angle-grinder/