I have some T-Rex heli flybars that are 3 mm and supposedly stainless steel, but they are magnetic so I'm not absolutely sure about them. I decided to get some 3 mm stainless steel round rod, which I found on ebay (coming from the UK.) I also bought a set of steel 3:1 gearboxes from rctank.de. They are the same width as the regular ratio gearboxes - much narrower than the mato 3:1, so I'm thinking it would be harder to bend those gear axles. The shipping from Germany is astronomical - 26 euros!