When to use inox (stainless steel) screws in an anchor as opposed to using galvanized/normal screw?
Inox is stainless steel with 10% (or more) chromium. The different grades have different alloys and create a stronger fastener. In industrial settings we do use A4 because it is superior. Think of case hardened for a parallel most think of in the U.S. do you really need the best grade? That depends on what you are doing high heat or cryogenic freezers may require a high grade but for home use I probably would not pay the extra. In fact depending on the type of fasteners needed you may have cheaper options with coated screws 1/10 the cost with 20+ year wearability. Although inox is stainless it can have iron oxide rust spots and if metal dust gets on the fastener in a damp area it can affect the material and can end up looking like a shiny rusted fastener. The difference I see with inox and galvinization both hot dipped and electroplated is after torquing a fastener in the contact point on galvanized parts may start rusting where with inox won't. It would help to know if you are talking about machine screws or wood screws to provide better comparisons.