They are often called Glass Drill or Tile Drill, but they are much more versatile since they are used to drill glass, tile bottles, ceramics, porcelain, ceramic tile, limestone, slate, marble, granite, light stone, and fiberglass.
The general rule is the smaller the diameter of your drill bit, the faster drill speed you can use. The harder your material, the slower drill speed you should use.

Please always remember to use water for lubrication, or the diamond core drill will burn. Not for use on Concrete or for depths beyond about 1/2".
Note: If you smell burning, back off! Either your speed is too high or the pressure you're applying is too much. Your drill bit should never be hot to the touch.

2Pcs 38mm/1.5inch Diamond Glass Drill Bit in a Pack
Material: Metal, Diamond Particles Coated
Hole Saw Diameter: 38mm/1.5inch
Packing Weight:120g
Packing Size:12x8x4cm