4" Wing Dividers

Wing dividers may look like a tool that you used in school to draw circles called a compass. Dividers essentially operate the same way just without the pencil. Although you can mark circles with them, they are most commonly used on leather for marking a straight border. 
Simply adjust to the width you want to mark, then drag one point along the edge of your leather while making a mark on your project with the other point. This is great for long straight borders like on a belt and a quick answer for marking all four side of project like a wallet without the hassle of lining up a ruler on each side.

Wing dividers are also great for quickly and accurately marking the distance between a line of holes to be punched out.