What is a cup cutter?
A cup cutter is a boring tool that looks like a pogo stick on steroids. By "boring", we mean that it is used to bore into the ground. It cuts a cylindrical core of soil four and one-quarter inches across. This is how those holes are made on the putting green. The cup-cutter actually isolates and cleanly removes a pineapple-can sized cylinder of soil. That cylinder of soil (like the center of a doughnut after it's removed) can be very useful. Don't forget, when a new hole (4-1/4 inches in diameter) is cut into a green, the previous hole needs to be filled. That cylinder of soil just happens to be the precise size!
How much cup does a cup cutter cut if a cup cutter could cut cups?
The USGA and Royal & Ancient Club both specify that the hole must be a minimum of 4-inches (100 mm) deep. However, a cup cutter must dig deeper than that to allow for the depth of the cup liner and the cup liner's flag stick socket.