This TALAtools 69547 Professional Diamond Tile Drill Bit, 15mm, has a diamond grit edged bit.
It is a slotted bit design for easy waste removal and is suitable for use with most power drills.
This diamond tile drill bit must be used with a water-based cooling system.
For use on porcelain, granite, stone, terracotta and ceramic.
There are four sizes currently available.

Specification:

Diameter: 15mm.