Annular cutters are hollow drill bits that cut only around the periphery of a hole. They reduce the torque and horsepower requirements for drilling because they remove less material than standard twist drill bits. Annular cutters produce accurate, burr-free holes without the need for pilot holes.
Hole-enlarging drill bits increase the size of an existing hole, and have no cutting points to start a hole. They are suitable for enlarging a hole up to twice its existing size.
Micro drill bits create very small or micro-sized holes. They are best used with high RPM, coolants to reduce friction and reduce heat, and a slow feed rate.
Reduced shank drill bits (also called Silver & Deming or S&D) have shanks that are smaller than the drill diameter, so they create holes larger than the typical chuck capacity.
Spotting drill bits are commonly used to start holes in a hard material. This pilot hole is used to guide another size of drill bit into the material. This leads to more accurate hole placement. Choose a spotting drill angle that is larger than the primary drill bit. For example, when using a primary drill bit of 118 degrees, a 120-degree spotting drill bit angle provides the best result.
Step drill bits are usually tapered, with steps of varying diameters like a pyramid. The smallest diameter is at the tip and the largest is near the shank. These are for use on thin materials such as sheet metal. Some step drill bits create either a countersink or counterbore hole, eliminating a separate cutting operation.
Taper shank drill bits usually have a Morse taper shank which is tapered from one end to the other. The taper for the bit fits into the taper of the spindle. The friction between the surfaces provides a secure holding system and accurate placement of the tool. This eliminates the need for a chucking tool holder.
Threaded shank drill bits can be screwed into a drill or drill attachments. This design is a chuck-less attachment that can decrease the overall length of the drill and drill bit so it can fit into confined spaces. Slippage with a chuck tool-holding mechanism is also eliminated.
Twist drill bits are end-cutting tools with two or more cutting edges and two or more flutes. The flutes brings chips up and away from the cutting edges and allows for coolant to reach the cutting edges. They are the most common type of drill bit.