The quality of the bits is pretty good for the price. These bits won't cut very many holes. But it should be fairly obvious from the price point. A good quality Bosch will cost you 2-3 times as much My problem with these bits is that they aren't deep enough to drill through a 1" thick granite slab. Sure, I read in the product description that they actually cut 1 1/4" thick material. This is what we typically refer to as 3cm material in the US. Hit the center of the ball with a hammer and dowel. Not perfect and might break the granite I got lucky and it worked with the minimum ly damage. These nozzles are suitable for 2 cm thick tiles and natural stone.