As a layman, how can I know the shear strength of a particular size bolt?

For example, if I want to attach something to the internal wall of my van ( 1mm stainless steel ) using a rivnut and standard metric bolt and it should hold up to 50 kg, how would I figure out the right size and grade to use? Nothing specialty, just standard stuff a layman could get at a typical hardware store.

In my specific case I'm installing wooden cabinets on the internal walls of my Fiat Ducato van, but I'd like as general an answer as reasonable.