The presser foot on the left is for my Toyota 21-DES -- a front-loading sewing machine. It has a straight needle hole. The presser foot on the right is for my Brother XR6600 -- a top-loading sewing machine. It has a curved needle hole.
Why? What difference does it make which way you put the bobbin into the sewing machine? Well, it's to do with the shuttle hook. In a front-loading sewing machine, the bobbin case and shuttle hook are vertical, and the left-right movement is in a straight line from the needle's point of view.
But with a top-loading rotary bobbin, the shuttle hook moves in a curve in front of the needle. For you to sew a zigzag, the needle must move forward a little at the sides or else the hook wouldn't come near enough to the needle to pick up the thread and form a stitch.
So that's why the needle hole is a different shape on front-loading and top-loading sewing machines (and their presser feet). And now I won't be getting feet for the wrong type of machine! I'd better go and check my Amazon wishlist to make sure I've got the right ones listed! : )
Until next time, happy sewing!
The Sewing Corner