Machined with granite as advertised. Perfect for us laypeople who need a tool once or twice and don't want to waste keg and keg on it. Just make sure you start drilling at an angle, take your time and don't overheat. I used plumber's putty to make a ring around the bit while drilling and fill it with water to keep the bit from overheating while drilling. The hole on the gaanite for installing a cotton ball kitchen faucet is the price of the kit.