Thunderbolt 3 cable

Hi DJOlynD, 

Thank you for using the Apple Support Communities. 

It looks like you want to know if you can use a Thunderbolt 3 cable with a USB-C external hard drive and we also see that you've already checked out the Apple Support article Adapters for the Thunderbolt 3 or USB-C port on your Mac. 

The Apple Support article About the Apple Thunderbolt 3 (USB-C) Cable states that you can use a Thunderbolt 3 (USB-C) cable to connect to USB-C device. 

We hope this helps.

Take care.

CAUTION:

The cable that shipped in the Box with your MacBook Pro is a CHARGE-ONLY cable. it has no high-speed data pathways at all. You can use it for a keyboard, but not much more.

Genuine ThunderBolt cables have a thunderbolt/lightningbolt symbol at each end.