There are three main types for presser feet to fit most sewing machines - screw-on or snap-on
Low shank - Most popular, most brands where foot height is 2cm
Slant shank - Singer Slant needle machines only.
High Shank - Some older models 15+ years
New style has quilting guide. Walking foot/ even feed foot, screw-on. For sewing hard to feed fabrics. Excellant for plaids, stripes, top stitching and quilting.
Spring-loaded needle clamp screw for walking foot, free motion foot & ruffler for machines where the needle clamp arm does not allow enough support for the activating finger of the attachment (important when using zig-zag).
For older Singer models,
Use for over casting the edge of fabric. Has small bar to help stabelize edge of fabric. Note: must set zig-zag width wider than bar (no guaratee for breakage)
FREE motion, larger opening for new 6mm width machines.
For darning, quilting, embrodery, monograming etc. allowes the operator to move the work freely while stabelizing the fabric, works by mounting in place of the regular pressure foot with a fork wrapped around the needle clamp screw for a spring movement.