..such as crevices, normal plumbing flux and although I have had luck with most solders, 4% silver bearing solder is stronger in the long run...kinda high priced tho... I'd Harris solder available at some time so no massive deal for me but high-priced if you don't want the energy for https://andyqsspn.theisblog.com/27477386/rumored-buzz-on-types-of-solder-to-use-on-aluminum-radiator