Originally posted by Digitalis * Which are made of what I take to be Brass: which is a bit perplexing as I thought the entire idea of using that metal was to avoid corrosion and cracking.
Brass/bronze is mainly used for its auto lubricating properties (e.g. phosphor bronze, a type of copper and tin alloy), and yes, in corrosive environments, too. It all depends on the specific alloy. P bronze doesn't seize up like, for example, aluminium, which tends to because its protective corrosion layer is harder than the base metal. It's rather the opposite because phosphor tends to form low friction molecules. It's used in your engine oil's additives to keep it running smoothly in place of the earlier, toxic, lead.
Avoiding cracking is another matter that depends on the material toughness, elasticity (elastic deformation, rather than the catastrophic plastic one) and cyclic stress limit of the alloy. You can't have it all in one, so you have to make compromises and choose the right one depending on the expected working conditions of the piece, plus a little leeway. That leeway depends greatly on costs and safety. For a non human endangering piece you would try to make it as low as possible to save on material and thus costs, but keep it in a statistically reasonable failure rate for the products price point.