a sewing machine for making buttonholes. Straight and round buttonholes are usually made with a simple shuttle stitch that cannot unravel. More elaborate buttonholes are made with a two-thread chain stitch, which creates a more attractive pattern on the edges. Sometimes in addition to the two threads forming the edges, a third thread is inserted under the stitch from the top side of the buttonhole, forming a ridge ensuring a firm finish.
Buttonholers that make the opening after forming the edges are usually used for knits and other fabrics that run easily.