Do I need to purchase a nano sim to micro sim adapter? Read description first?

I bought a prepaid SIM card that has three formats: one big sim (I think it's a macro sim), the micro sim and then the nano sim. It is the type that you just press down and get the right cutout you need. I kept the micro sim layout and am currently using a nano sim on my iPhone. So can I just put the nano sim into the micro sim layout? I really don't want to buy a sim adapter due to all the horror stories of them breaking your phones sim tray. Please provide an explanation and don't just say yes or no and nothing else.

Its miniSIM (what you called macroSIM), micro & then nano.

You'd of course have to use what size SIM the iPhone (didn't specify which) takes.

original, 3G, 3GS - miniSIM
4, 4s - microSIM
5, 5c, 5s, 6, 6 Plus, 6s, 6s Plus, 7, 7 Plus - nanoSIM

Yes, it's fine.

Put the SIM on a flat surface and press the appropriate frame it came out of back down over it.
That avoid the SIM getting flexed, which can happen if you press on that.

Just make sure the edges are flush before you use it.