"Walking foot" is a generic term for alternating presser feet. The feet for this type of machine are in two parts, and ride on two separate shafts. When the outside part of the foot is down, the inside part of the foot is up, and vice versa, hence the name alternating presser feet. An industrial machine with a "walking foot" has three vertical shafts, two for the foot and one that holds the needle like in the picture. These machines almost always have compound feed, which means more than one type of feeding system. In this case, it refers to drop feed, which employs feed dogs, and needle feed which should be self explanatory.
The machine needs to have the three vertical shafts or it is not a walking foot machine. That being said, there is no attachment of any kind that will change a non walking foot machine into a walking foot machine, so don't waste your money.
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