Hi, April. You've received a lot of feedback already. It does resemble the "Walking Foot." I remember the ruffler foot also. The ruffler foot looks similar to the walking foot, but with one additional feature: it has a little claw that swings according to whatever adjustment you make on the body of the foot. The claw swings to grab a measured portion of fabric into a pleat while the sewing advances. It repeats according to the frequency you set on the foot's adjustment or stitch length setting. Your mystery foot looks like it has adjustments for ruffling on it. Experiment. If it is a walking foot, it will make matching plaids, stripes and patterns more accurate in the stitching. If it is a ruffler, you will find your fabric neatly and uniformly pleated as you stitch. If it is a side cutter, then I guess it will trim as you sew. If it is an elastic sewing foot, then feeding elastic through the slot and sewing it to the fabric will be successful and easier. Whatever kind of function it performs, the short fork installs on the presser foot bar shank screw. The long fork sits on the needle bar clamp screw. Both screws must be tightened securely. You may set your stitch width for zigzag or straight stitching. Have fun! Let us know what you find out! :-)!