Not entirely aluminum and not smooth at all. I used some fairly light oil in them and found them pretty bad - they don't really improve the plastic shock absorbers of the simplest models just in cosmetics, not in functionality. They are nowhere near as good as the Slash Platinum shocks and feel less smooth than the plastic based shocks. I often change pistons to tune shocks and tune my suspensions, but I wouldn't waste time doing it. There's nothing wrong with going for a cosmetic "upgrade", but I love the functionality over the shape of my RC trucks. You'll probably end up with a robot project where very little damping is really needed.
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