YUERONG 4-1/2 Inch Hole Saw HSS Bi-Metal Hole Saw Bit M42

A hole saw (also known as a hole saw), also known as a hole cutter, is a circular (ring) shaped saw blade whose circular cut creates a hole in a workpiece without cutting the core material. It is used for drill bits. Hole saws usually have a pilot bit in the center to keep the teeth from moving. In fact, hole saws can make holes without cutting the core, so twist drills or spade drills are often better suited for relatively large holes (especially holes larger than 25 mm (1.0 in.)). The same hole can be punched faster with less power. The depth a hole saw can cut is limited by the depth of its cup-like shape. Most hole saws have a fairly short diameter-to-depth aspect ratio, and they are used to cut relatively thin workpieces. However, longer aspect ratios are available to warrant their application. Cutting with a hole saw is similar to some machining operations, known in the industry as nesting, which oscillates the knife like a throwing knife to achieve similar results and full cores as ring cuts.
(from Wikipedia)