This can be a point of confusion, just what kind of sim card a certain phone uses and how to get such a sim card.
4-5 years ago the standard sim size was Mini, which around 2 years ago got moved into Micro and now Nano is getting used.
HTC started with Micro sims around 2 years ago in the 2012 One family of phones (One X and One S, followed by One X+). One V used a Mini sim.
The 2014 HTC One M8, One Mini 2, Desire 816 and Desire 610 all uses Nano sims.
So, if you have a larger sim card you of course need to get the smaller kind.
But, I can’t find a Nano sim in my country/network. Help!
If they haven’t adapted at all for the newer iphones (since they all uses nano sims): you can actually cut down a Micro sim into a nano sim, just make sure that it’s the newer type of the sim so the actual circuits will fit on the nano sim. Do NOT try to cut those older Mini sims into Nano, since that will just fail. Nano from a Micro will work, Nano from an older Mini will NOT work. There’s sim cutters you can use for this, that doesn’t cost very much
But, I have a smaller sim and I need a larger one. What do I do?
Then you need to get a sim card adapter. There’s plenty of those around in the various sizes you could need. On the picture you see the variants needed: Nano to Micro, Micro to Mini and Nano to Mini.