What is Nano-SIM?
Fourth version of SIM card or the "fourth form factor" (4FF) of the SIM standard. Size is at a mere 12.3 mm by 8.8 mm by 0.67 mm, but still holds the same amount of data as earlier SIM cards.
Nano SIM is smaller and about 15% thinner than Micro SIM (3FF). Technically, the original SIM (1FF) card standard is the same size as a credit card and most people probably have never seen one in person.
Nano SIM reduces the size of the SIM to the gold contact area and has just enough extra insulating "card" around it to prevent electrical shorts
Photo Credit: Wikipedia (Justin Ormont)