This is a very simple garter rib mitt. It is worked flat and seamed afterwards. You choose where you wish the thumb opening to be and how big an opening you want. It is very stretchy. The S/M will fit most people, but people with larger hands may appreciate the extra stitches of the L/XL.

The picture shows two mitts from the e-book The Magic of Three. The Beauty of Simplicity is pictured on top, while Cables All Around is on the bottom.