The first question to answer is how old is your machine? Most machines made since 1980 use snap-on feet (Except Berninas, which have their own style of attaching, and therefore need an adaptor).
Does your machine's foot screw on or snap on? If it doesn't use a screw to attach, then it's a snap-on.
If it screws on it is important to know whether your machine is a low shank, high shank, or slant needle machine. If you are not certain, you can measure using the simple instructions below:
To Measure: When presser foot is down, measure the distance from the bottom of foot to screw-hole that holds the foot onto the presser bar.
TIPS