Types of Drill Bits, Starting With the Twist

Most likely the first drill bit you’ll encounter in your carrier is a twist bit. These are the bits that saturate hardware stores and garage shelves of the Do-It-Yourselfers. They are a good introductory bit to analyze. So let’s dive in…

Here is an example of a typical twist drill bit:



The part that goes into the clamps of the drill is called a shank. There are different shank types as well, but we’ll talk about those later (but as a matter of curiosity satisfaction, the shank on this picture is labeled very creatively -- “straight”).

The rest of it is the body of the drill bit.

The spiral in-cuts are called flutes.

The end tip is called a point.

That was easy.

Now, twist drills generally come as single-flute drill bits or two-fluted drill bits. Both types are used for originating holes. The two-flute type is the most commonly available.

There are also three-fluted (core) and four-fluted (core) drill bits. Those are used interchangeably to enlarge existing holes.

There are also different length ranges. Below is a representative picture of some common lengths.


(click on the picture to enlarge)

Screw Machine Length Drill Bits
These have short flutes and short overall length. They are commonly used on sheet metal. Screw Machine bits are also called “stub length drills” or “stubbies”.

Jobbers Length Drill Bits
This is the standard length used for general purpose drilling. For this bits, the length of the flutes is ten times the diameter of the drill.

Taper Length Drill Bits
These are a little longer than jobbers length bits.

Extra Length Drill Bits
These come in various sizes, and are frequently used in automotive/aerospace industries, and in conditions where the target is hard to reach.

Longboy Drill Bits
These have longer flutes than extension bits and are available in larger diameters.

There are many different variations by different manufacturers, targeted towards unique projects. So always inspect catalogues for options, when settling on size.

One last aspect of twist drills I’d like to cover in this post is right hand drill bits versus left hand drill bits. Left hand bits cut in the opposite direction, and primarily used in large scale manufacturing for efficiency purposes. They are also sometimes used for removing screws. But those would be special screw removal bits…