However, it's very difficult to drill perfectly aligned holes into the two pieces, one millimeter of offset and you can be sure that your pieces will not be aligned as you want them to be. This is where dowel jigs are very useful : they help you to drill perfectly straight AND aligned holes between the two pieces, and their use is really easy. In this instructable, I'll show you how to make the simplest dowel jig of the world, with even two sizes of dowel. Let's work !