This is a non-abrasive Ceramic media. These can be used when tumbling rock to act as a grit carrier and filler to aid in grinding and polishing of the stones in the tumbler.  They are angle cut cylinders measuring 5/32″ x 5/16″and can be used in all steps from start to finish.

They are reusable and can also be used as a Burnishing Media for jewelry items.  They require about a 24 hour break in period before using them for burnishing metals.

Not sure if these are your best option for filler media?