Comprehensive Guide to Drill Bits

These drill bits are also called twist bits or metal drill bits and are by far the most used type of drill bits. They're best suited for everyday uses and drilling through a wide variety of metals, plastics and wood. Most feature a cylindrical shank although you can also find some with a 1/4" hex shape for use with an impact driver of screwdriver. These bits stand out from others because they have a black color. Some HSS bits are coated with titanium or cobalt (explained below). While these coated bits are more expensive, they have a much longer life. (Image courtesy of Jordanhill School D&T Dept at Flickr)

Cobalt HSS bits are ground carefully from solid cobalt high speed steel (HSS) which makes them incredibly resistant to both abrasion and very high temperatures. For this reason these bits are designed for material like weld seams, cast steel, cast iron and stainless steel.

Titanium drill bits feature a coating of titanium nitride for a longer cutting life. This coating lowers the level of heat build-up and improves lubricity (a measurement a lubricant's ability to lower friction). These bits are similar to an HSS bit as they can be used on plastic, metal and wood but they have a life up to 6 times longer.

These bits have a sharp tip called a W-point or brad point tip. This means the outside edges of the drill with cut a diameter for the hole before the center is even broken so a clean hole is produced. These bits are designed mostly for drilling into wood and often include depth stops so you can select the right depth for the drill. You'll find these bits come in many sizes and lengths.

Will you be drilling into stone, brick or concrete? If so, you'll need a set of masonry bits. These tools have a tip coated with tungsten carbine (may or may not be a different color) and they are meant to be used with a hammer drill. It's very important to realize that these bits will cause a lot of heat to build up so make sure you use the right drill RPM and take the bit out often to clean off the flutes. If possible, select masonry bits with a chrome-vanadium shaft for a longer life.

These bits are designed for making large holes in wood and most have an extension shank and a 1/4" hex shank. Like the auger bits below, these are very common drill bits for anyone working with wood. They also go by the name of paddle bits because they have a long, flat design with a pointed tip that starts the hole. You'll notice they have the size etched into the paddle.

Image credit: Phrakt at Flickr

Auger bits are used to make a deep and large hole. They have a spiraling shaft that ends with a very sharp point. They are one of the most common types of bits for wood and work best on very hard timber. Most have a hexagonal shank so there's better connection between the drill bit and the chuck of the drill. Make sure you select auger bits made from carbon-steel, as it's much easier to sharpen in the future.

These bits are designed for one specific purpose: creating concealed hinges. They have a flat-bottom shape that helps you stop right before you go through the wood. Some forstner bits have a continuous rim, which works best if you want a small hole. For larger holes that are a little rough, you'll want a saw-tooth rim on the forstner bit.

Image credit: Public Domain Photos at Flickr

While the bits above are the most commonly used forms, there are quite a few other types out there you may need. These include:

• Countersink and Drill/Countersink Bits - Countersink bits can drill a hole as well as cut space out of the material. They're used to keep wood from splitting as you drill. A drill/countersink bit, on the other hand, works like a countersink bit as well as an HSS bit. They're designed to drill pilot holes for the a countersunk screw.
• Spear Point (Glass and Tile) Bits - These bits have a unique tip that really does look like a spear. This spear end is made from tungsten-carbine so it will go through glass or tile and make a hole as large as the base of the spear tip.
• Special Drilling System (SDS) Bits - These specialty drill bits are made to fit an SDS chuck and won't work with other drills. You'll notice they have a unique end with a regular-looking shaft.
• Step Drill Bit - These bits have a very unique shape that looks like a staircase or a step pyramid. This allows you to use a single bit to get different hole sizes. They work best on soft material that's very thin. This bit is similar to the conical bit, although it has the notches cut into it.
• Plug Cutting Bit - Plug cutters are specialty woodworking bits that cut out plugs that will be used to cover screws later. These bits have a very noticeable opening in the side that allows the plug to be taken out.
• Saw Bit - This bit may be called a hole cutter bit or a hole-saw and it's designed to cut both metal and wood. The drill bit in the center will cut the hole first and the round saw cutter will make the hole much larger.
• Multi-Purpose Drill Bits - Multi-purpose bits feature a diamond-ground tungsten carbine tip that allows them to drill through nearly everything, including metal, tile, wood, masonry and plastic.

As with most hand tools and accessories, choose a high quality set of drill bits and take care of them! Make sure they're always put back clean and dry in their case and don't let them roll around in a cabinet drawer or toolbox, as this can damage the cutting edge. It's important to select a set that includes the type of bits you'll use most often and only use them for their intended purpose. HSS bits, for example, last longer when they're used only for working with metal versus metal, plastic and wood. Some sets only include bits of the same form but you'll also find sets with a variety of bit types to tackle many jobs.

Because these tools require occasional maintenance and special care, it's important to select a set that includes a durable toolkit that keeps your tools safe. This picture shows a Multibox set of bits from Bovidix, a system that's both space-saving and efficient.

It's also a good idea to learn how to sharpen the bits yourself and do it every so often, not just when the bit becomes very dull. Some drill bits are not easy to sharpen, though, because of the shape of the spur points.