My treadle sewing machine manual describes it as a ruffler, and it automatically makes tiny pleats in either ribbon or fabric, if in ribbon it can be used to pleat and apply in one go. The plates allow the ribbon to be pleated whilst the fabric layer is moved past using the feeddogs. Usually there is a cam that can be adjusted to make larger or smaller pleats .. but the pleats are fairly neat and small even at the larger setting. I regularly use mine to sew with on my bernina .. I bought it a singer to bernina attachment foot and it works well. My treadle dates from the 1880's ... and is a singer .. although I suspect there were many many of these made and sold and not all were for singers.