How to tell if a USB-C cable is Thunderbolt You can't tell by looking. Not reliably. The cable knows what it is. There's a chip inside the connector called an e-marker that declares its capabilities, and your Mac can read that declaration. The trick is getting it back out in a form you can use. Three ways to do it, worst to best. Method 1: look at the connector (mostly useless) Every guide on the…