In article
,
John Husvar wrote:

Some of the best wheelchairs in the world, except it can be damn near
impossible to work on one. Why? Because they habitually use hardened,
black oxided, fine thread, steel Hex Head Cap Screws in aluminum
assemblies! Dat's Why!

Let those parts go for a couple of years and the aluminum and steel both
corrode and bond to each other stronger than a weld. It has too often
become necessary to drill out the steel screw and replace it with a
through bolt--Or just replace the entire assembly--If it can be taken
off at all-- dying--alone--in the rain. (Oops. Disregard that last:
Hemmingway Syndrome. Sorry.)

Can't heat them because they're usually in places on the wheelchair
where doing so would ruin some other vital subassembly.

IIRC, nitric acid dissolves steel and not aluminum.

--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/