tim-b wrote:Hi
If the bolt is stainless steel that is, by the way, very bad for corrosion of the alloy, because chrome and aluminium are a long way apart in the electrochemical series
The electrochemical series is an indicator of risk and needs to be looked at in specific situations, which interests me on a practical level because the ratio of cathodic and anodic areas is another factor in area-related cell current. The small surface area ratio of the cathode to a large surface area of the anode, e.g. a stainless bolt in an aluminium alloy component, will minimise corrosion
Time spent wet is another factor and a stainless fastener in an aluminium alloy component is generally compatible with a bicycling environment; it's a combination used practically to hold aluminium bridge panels to roadways.
Totally agree with all that, but I think you're forgetting the detail of the original post. This involves a fastener that needs to be unfastened and refastened. Unlike those bridge bolts, which like the stainless screws holding my greenhouse together do NOT corrode the alloy structure at large, but merely acquire a bit of white stuff arorund their heads and threads that actually helps prevent them coming undone. That's fine for my greenhouse, that I have no desire to dismantle. The OP on the other hand, would very much like to adjust his wheelchair/cycle adapter!
But anyway, he doesn't have a stainless bolt like you suggested. What he has is a rusty plain steel bolt and that'll be fine so long as he greases it up with one of the specific corrosion-inhibiting compounds I mentioned. Even lithium grease would be okay if re-applied regularly, before it has a chance to dry out. Trouble is, people let sleeping dogs lie. So better use something one can safely fit and forget.
As an aside...
I'm glad you mentioned the anodic-cathodic area thing. My shittyest example of that in bicycle design is when SKS acquired ESGE's Chromoplastic mudguards. These originally had solid alloy rivets in stainless bridges. A poor combination because the rivets are small and the bridge plates quite big, but okay in practice because the rivets are big enough to just get a bit furry, and long and fat enough, being fattened even more by the simply-hit-it-on-the-end rivetting method, to still hang on in there. I still have a pair of these mudguards on one of my bikes at least 30 years old. Though to be honest I never rode that bike much in the winter.
But SKS had a differrent rivetting process. They used rivets with a hollow end that was spread out thinly around the hole by a pointed rivetting tool. Initially SKS used stainless rivets in Chromoplastics and this was fine, except that the alloy foil encapsulated within the clear plastic guard made contact with the stainless rivets and consequently corroded around them due to glavanic action, once exposed to wet and salty winter roads. This corosion was harmless, but unsightly. I still have a pair of these gaurds too, some 25 years old, on a bike I commuted daily on for most of those years.
But if things get unsightly without breaking: they hang around looking bad all the while, which is terrible for future sales. So SKS quickly changed the rivet material to alloy. This was also lighter and much cheaper, not only to buy but also in wear on the rivetting head. Marketing and accounts must've been ecstatic. And after all, hadn't ESGE used alloy rivets? But the hollow end of the SKS rivet provided a perfect salt-cellar, and the thinly spread alloy, in wet contact with a relatively large area of stainless steel, quite rapidly rotted. But not too rapidly. It took a couple of winters after the change before we started to notice the bridges falling off SKS mudguards. And cyclists' expectations of durability had by then shrunk dramatically - especially when it comes to things that are nowadays viewed as 'mere accessories'. And broken things disappear. So SKS pretty much got away with what I considered a quite apalling reduction in product quality.
) and was a bit nicer to look at. That didn't preclude the use of grease on the threaded area for ease of adjustment (although I didn't specify that)
