Different size SIM card trays?

All I need to do is set up an iPhone 6S I just got to be used on wifi only. It doesn't have a SIM card, or SIM card tray. I tried to put the card/tray in it from my iPhone X (solely to set the phone up, I'm keeping the X in service), but it doesn't seem to fit. My eye thinks the card is a millimeter or two too big. Is this true? Did they change the size of the tray?