While I cannot speak to the thickness question, however you have to be careful when combining two dissimilar metals like steel and aluminum it is possible you can get some pretty bad corrosion to the aluminum. Since you will be using stainless I cannot say if this will be an issue or not.boomn said:I'm fixing up a junker aluminum SS frame that has pretty chewed up track ends. My plan is to not only file the dropouts smooth again but to also remove just enough material from the inside faces to add some steel plates. Dropouts are ~7mm thick and I would need to get them down to 6mm anyway to smooth out the deep indents, so I was thinking of using 20 gauge 304 stainless. Does 20 guage sound thick enough to last or should I use something thicker? Does 304 sound appropriate for this?