HTC One M8 for Windows - Manual (Page 22)

nano SIM card
HTC One uses a nano SIM card.
Use a standard nano SIM card only. Inserting a modified card that is thicker
than the standard nano SIM card may cause the card to not fit properly or
damage the card slot.
Inserting a nano SIM card
1. Hold the phone face up.
2. Insert the tip of the tray eject tool into the tray eject hole next to
the nano SIM card slot.
22 Unboxing