""Bought these to drill rock hard Italian porcelain tiles to put up radiator in newly tiled en suite, use lots of water via a spray bottle ( I used an old one from kitchen detergent spray) keep spraying as you drill and stop and spray into the hole every now and then to clear out debris, start the hole off with pointed type drill for porcelin ( Screwfix part number 53634 for example) ,done 4 holes without any problem, still looks good for more, excellent value for money considering the cost of other types on offer."
"... you have the water dispenser coming from other more expensive drill bits, otherwise it is impossible to keep it cool and wet! There is no pocket on the shaft so the water don't cool the inside and it's a pain to empty the bit from the previous tile. However if your porcelain is not a Grade5 like mine you should find a good value for money. "Adjust" your manual drilling pressure as "medium" and don't use too high speed on the drill, suggested 50% of the max drill speed."