A hole saw (also styled holesaw), also known as a hole cutter, is a saw blade of annular (ring) shape, whose annular kerf creates a hole in the workpiece without having to cut up the core material. It is used in a drill. Hole saws typically have a pilot drill bit (arbor) at their center to keep the saw teeth from walking. The fact that a hole saw creates the hole without needing to cut up the core often makes it preferable to twist drills or spade drills for relatively large holes (especially those larger than ). The same hole can be made faster and using less power. The depth to which a hole saw can cut is limited by the depth of its cup-like shape. Most hole saws have a fairly short aspect ratio of diameter to depth, and they are used to cut through relatively thin workpieces. However, longer aspect ratios are available for applications that warrant them. Cutting with a hole saw is analogous to some machining operations, called trepanning in the trade, that swing a cutter analogous to a fly cutter in order to achieve a similar result of annular kerf and intact core. Construction The saw consists of a metal cylinder, usually steel, mounted on an arbor. The cutting edge either has saw teeth formed in it or industrial diamonds embedded in it. The arbor can carry a drill bit to bore a centering hole. After the first few millimeters of cut, the centering mechanism may no longer be needed, although it will help the bit to bore without wandering in a deep hole. The sloping slots in the cylinder wall help carry the dust out. The kerf of the cut is designed to be slightly larger than the diameter of the rest of the hole saw so that it does not get jammed in the hole. Holes saws for use with portable drills are commonly available in diameters from 6 to 130 mm, or in the US, ¼ to 6 inches. The only limit on the length of the cylinder, and thus depth of the hole, is the need to remove the bit from the hole to clear dust. A cylinder length is not uncommon, although shorter bits are usual. By breaking the core off from time to time and using a shank extension, a diamond core drill can drill to depths many times