There are two types of micro-to-mini adapters I have seen, and I suspect both types exist for nano-to-micro/mini. I have type B) nano-micro and nano-mini adapters

Either
A) the adapter has a whole cut out, with a tiny bit of lip at corners to hold the smaller sim card, or
B) the adapter has an indention the size of the smaller sim card.

Type A does not increase the thickness of the overall resultant SIM, while type B does. Type A holds the sim a bit more securely, the lips on Type B tend to be quite small..

Type A is better for micro-mini adapters (I have had issues where the extra height causes extra wear on the sim slot pins). Type B is better for nano adapters because you want the extra material in the adapter to make up for the thinner nano sim.

I have destroyed the sim slot on a phone while using an adapter and am now very careful plus somewhat reluctant when using adapters.

Sorry for this extremely long winded reply