Laser Distance Meter.

[AliGage]

I may well be using them wrong lol but these are cheap and have lasted ages.
I think maybe its my angle grinder too aggressive maybe I don't know.

Aggressive how? They're supposed to be used at high speed

 

[cbmltd]

I don't know,I got about 8-10 holes
15mm was using them dry which your supposed too,maybe I should of used water ??

 

[Old Mod]

@cbmltd
Read this
Apply the technique to your grinder dry bits, as you drill the tile use a slight oval motion with the grinder, don't just push through in a downward motion, rock it if u will!

Tiling tips 2015

 

[AliGage]

I've had one of the Rubi 20mm bits for about 8 months now. It'd bored through all materials and I've literally just done two wholes in marble this morning.