Originally Posted by
dddd
Slippage at the clamp is dangerous and was not uncommon during the ~26mm bar clamp days.
Pop cans (most cans, actually) are poly-coated on both sides, and this greatly affects the surface coefficient of friction. The coating can be sanded off easily.
Larger-diameter beer cans like Fosters are necessarily made of thicker aluminum, so if you have a caliper you can determine how many fewer layers/wraps are needed.
I have a screw-top can of nitro-brewed coffee here that is made of some thick aluminum, no way you could crush this can easily!
DDDD has some good points here... I don't have any knowledge of the finishes applied to various aluminum containers created for food stuffs, but his idea of them being coated sounds plausible. That's why having an aluminum shim material (so there is no issue of dissimilar metal corrosion) and being able to sand off any possible nefarious finish is a bonus (in my thinking). I've noticed that various thicknesses of food containers are out there, as various companies use different suppliers for their containers. You can always take a magnet into the store with you (to weed out the steel cans). Anything non-magnetic is almost assuredly aluminum.