Makes the sewing of blind invisible hems easier on the sewing machines, using guides in the foot.
The model of your machine will dictate which foot option is used, either the adjustable or fixed.
Category A - this is the adjustable option and the guide can be control by turning the screw to bring the guide closer of further away from the fold in the hem.
Category B,C and D - this fixed option has a metal guide in the centre which fits snugly to the fold of the fabric in the hem. The needle moves left to right over the metal guide creating slack in the stitch to avoid a puckered, pulled stitch on the right side.