From the people who first brought you sapphire inserts:

Made from pure optical grade sapphire, and highy polished.

24mm outer diameter (some 30mm bangers with 2-2.5mm walls will have shrinkage or imperfections blocking them from perfect fits - please measure if you are unsure)

20mm height

2.5mm wall thickness

3.5mm base

Careful tapers at every edge, rounded junction of wall/dish for easy cleanin