I found a manual for this machine. It's a buttonholer alright.
Singer 71-101 and 71-107 High Speed Gear Driven Feed Sewing Machines are designed for making straight buttonholes in cotton, linen, rayon and silk fabrics, knit goods, etc. These machines have a positive, gear driven, intermittent feed which controls the movement of the work clamp so that the stitches are uniformly spaced around the buttonhole under all conditions.
http://www.manualslib.com/manual/364...01.html#manual