A zigzag stitch is variant geometry of the lockstitch. It is a back-and-forth stitch used where a straight stitch will not suffice, such as in reinforcing buttonholes, in stitching stretchable fabrics, and in temporarily joining two work pieces edge-to-edge. When creating a zigzag stitch, the side to side motion of the sewing machine's needle is controlled by a cam. As the cam rotates, a fingerlike follower, connected to the needle bar, rides along the cam and tracks its indentations. As the follower moves in and out, the needle bar is moved from side to side. Sewing machines made before the mid-1950s mostly lack this hardware and so cannot natively produce a zigzag stitch. However there are often shank-driven attachments available which enable them to achieve a similar effect by moving the fabric from side to side instead of the needle bar. Helen Blanchard is said to have invented and patented the first zigzag stitch sewing machine in 1873. The first dedicated zigzag machine for the consumer market, whilst many assume was the Singer 206K, introduced in 1936, was in fact the Necchi BU, introduced in Italy in 1932. Zigzagger attachments Older sewing machines designed to sew only a straight stitch can be adapted to sew a zigzag by means of an attachment. The attachment replaces the machine's presser foot with its own, and draws mechanical power from the machine's needle clamp (which requires the needle clamp to have a side-facing thumbscrew). It creates a zigzag by mechanically moving the fabric side to side as the machine runs. The zigzagger's foot has longitudinal grooves on its underside, facing the material, which confer traction only sideways. This allows the zigzagger to move the material side to side while the machine's feed dogs are simultaneously moving the material forward or backward in the usual manner. Singer zigzaggers Singer produced a variety of "Singer Automatic Zigzagger" attachments over the years, including part numbers 160985 and 161102. These zigzaggers are equipped with pop-in cams (called "Stitch Patterns") for making four different zigzag stitches, as well as a bight control for choosing the zigzag width. Four cams are included. There are also sets of additional different cams, four cams per set, sold as "Singer Stitch Patterns for Automatic Zigzagger". All cam sets are Singer part number 161008, and contain the following cams: * The #2 red set is included with the 160985 and 161102 zigzaggers. **