Brother XR-3140 repair/ replacement parts.  Low shank ankle, "J" zig zag foot and mounting screw.  Snap on style foot.
Genuine Brother replacement part. General purpose snap-on 7mm width zig-zag foot with "hump-jumper" button. When a rise is encountered, simply tilt the foot and push the button to set the foot. The foot automatically releases on it's downward slope. Price includes shipping to lower 48, return for refund if fails on your low shank machine.