yeah, rust buster, but your better off to get phosphoric acid(main ingredient of rustbuster, ferropro etc...) from a chemical supplier(maybe glendale packaging? i know they do sulphuric) in bulk... like 2 litres... then find a tub big enough to hold the whole frame... fill it up with water, add the acid....will take every little bit of rust off everywhere, especially those places you cant get into... then the whole surface will be nicely etched and ready for the primer