Mechanical sewing machines for stitches using gears and levers. One of the most important and creative of those gears is the Cam. A single cam looks like a small cookie with bumps and bites around it outer edge. Some older machines were designed to accept one cam at a time to produce a single alternative stitch. Gradually sets of cams were mounted together in a stack called a cam stack. The cam connected to the upper drive shaft and turned around as the shaft rotated. A lever called a cam follower or tracker was mounted perpendicular to the cam. As the cam turned the lever would move in and out along the bumps and bites of the cam. Connecting levers transferred this action to control the needle bar movement and create stitches. The stitch selector moved the follower to align with the edge of the cam to produce the desired stitch.