A holder for 1.5 inch ball bearings used as a weight inside filament spools. I didn't have a good storage solution to have them readily available on my workbench without them rolling away, so I made one.
Purchase link:
5Pcs 1.5''inch Bearing Balls Steel Ball Bearing 38mm Assorted Loose Bicycle Bearing Balls 1-1/2": Amazon.com: Industrial & Scientific
As seen here: