its length. Saw teeth are used for most materials, such as wood, plastic, soft plaster, and metal. Diamond hole saws are used to bore holes in brick, concrete, glass, and stone. Types Adjustable An adjustable hole saw consists of a number of thin metal saw blade-like strips, and a flat disc with a large number of grooves in one side and a shank on the other. By snapping the blades into different grooves on the disc, a hole saw of a wide variety of sizes can be constructed. Circle cutter Another type of adjustable hole saw, also called a circle cutter, is formed by having one, two, or three adjustable teeth on a platform with a pilot bit. To cut out a hole of any size, the teeth need only be adjusted to the proper position. This type is available in sizes up to and larger, and can be used to accurately cut large circles. Advantages and disadvantages The main advantage over conventional drill bits is the hole saw's efficiency, because very little of the total material being removed is actually cut, which ultimately reduces the overall power requirement. Another advantage over drill bits is the wider size capability. For example, a hole would require a huge twist drill or spade drill, unable to be properly driven by a pistol-grip drill or benchtop drill press; but it can be cut with a hole saw with relative ease. Some disadvantages include: The portable drill used must be capable of producing considerable torque at low speed They tend to bind if choked with dust, or if allowed to wander away from the central axis of the planned hole The kick-back from a powerful drill may be severe under some conditions, and long side-handles should be used, preferably with two operators for very large holes. The core plug often binds inside the hole saw, and often must be pried out after each hole is cut. Sometimes the prying is quite difficult. Sometimes the core plug will twist apart mid-cut, creating a condition where the core inside the hole saw spins on the yet-uncut portion of the core still in the workpiece. This tends to stop the cutting action of the saw, and if the workpiece is wood or plastic, the friction will start to singe it, creating a burning smell and heating up the hole saw. The twisted-off core must then be pried