I thought about more then two options. For example when you have 10 TV or Radio Channels. They are numbered from 1 to 10. And only one channel can be chosen. Or for example, you can buy concert tickets, maximum is 4 per purchase. You may want radio buttons with a number from 1 to 4. Or you have to choose a color or size for a t-shirt (Mostly they look like buttons but there functionality is radio).