If the zipper foot says it will fit a Featherweight, it will not fit your 301. The Featherweight takes low shank feet, and the 301 takes slant shank feet.
The vintage zipper foot I have for one of my 301s is #161166 and the other one is #160689. Look for one of those numbers and it should fit.
A Singer 533 is a stylist model, built after Singer started using plastic gears. Could be trouble if the gears are crumbling by now. I'd avoid it.
Last edited by Skyangel; 09-24-2012 at 03:26 AM.