*Red Box (Old Style) - for machines manufactured from 1954-1998 Top of the shaft has 2 posts and the back is rounded.
New Style the shaft has been squared off and has a solid post on the top front. These come in 3 Styles:
5.5 mm Style Feet or Classic ( Some will work on 9mm machines) 'C' Style Feet which are for 9mm machines and are Coded 'D' Style Feet which are for 9mm machines and are for use with the Dual Feed feature
Not all Feet come in all styles (available styles listed under each foot).
Check out this video on the differences in the feet. Click here