The iPhone 5 is an older model of Apple's smartphone, released in 2012. When it comes to the SIM card used in this device, it is important to note that there are two versions of the iPhone 5: one with a standard SIM slot and another with a smaller Nano-SIM slot.

1. **iPhone 5 (GSM models):** These devices use a Micro-SIM card. A Micro-SIM is smaller than the traditional SIM cards used in earlier phones but larger than the current Nano-SIM cards found in newer iPhones. If you have an iPhone 5 (GSM variant) and need to insert or replace a SIM card, ensure you have a Micro-SIM provided by your cellular service provider.

2. **iPhone 5 (CDMA models):** Although CDMA models don't typically use SIM cards for activation on CDMA networks like Verizon or Sprint in the United States, some CDMA iPhone 5 models do have a Micro-SIM slot for international use or when roaming on GSM networks. If your iPhone 5 is a CDMA model and you plan to use it outside your home country or on a GSM network, you'll need a Micro-SIM from a compatible carrier.

3. **iPhone 5C and 5S (all models):** It's worth mentioning that if you meant to ask about the iPhone 5C or 5S, both of these later models introduced in 2013 use a Nano-SIM card, which is even smaller than the Micro-SIM used in the original iPhone 5.

In summary:

- **iPhone 5 (GSM models):** Use a Micro-SIM card.
- **iPhone 5 (CDMA models):** May require a Micro-SIM for international use or on GSM networks.
- **iPhone 5C and 5S (all models):** Use a Nano-SIM card.

If you need to obtain or replace a SIM card, contact your cellular service provider, who will provide you with the appropriate SIM card for your specific iPhone model and activate it on your account. Make sure to handle the SIM card carefully, as they can be delicate and easily damaged. Insert the SIM card into the designated tray in your iPhone, following the instructions in your user manual or online support resources.