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 3/8″ x 5/8″ and can be used in all steps from start to finish.

They are reusable and will last for a long time.

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