These countersinks work great. The drills are conical and drill clean holes. They seem very strong and have outlasted me for well over a year doing odd jobs as a hobby. There are two screws on the table top that can be loosened. You can then adjust the worktop to the desired depth. The drill and base are one piece and the countersink is the other piece. Countersinks can also be used with conventional drills. You lose a lot of length if the drill has no base. The included extra Phillips bits are of decent quality but they are utterly useless. Who doesn't have a pile of these baits lying around anyway? The countersink needs base drills if you want to replace them. Otherwise they will be short. All countersinks are the same size with different size bits. Regardless of the hole size, the hole for the screw head is the same.