Connect a Mac that has a Thunderbolt 2 port to a device that uses usbc

If you need to connect Thunderbolt 3/4 devices to your 2013 Mac Pro, you can use the Apple Thunderbolt 3-to-2 adapter. It is a bi-directional adapter. The most obvious uses are for connecting TB 3/4 docks or connecting PCIe NVMe SSDs in TB 3/4 enclosures.

Caveats:

• The adapter only converts Thunderbolt protocol. If you connect it to a Thunderbolt 2 host port on your Mac Pro, the Thunderbolt 3 side will not offer USB-C (USB, Power Delivery, DisplayPort).
• Some peripherals (like 5K/6K displays and eGPUs) might not work well, or at all, with a TB2-equipped Mac – even with the aid of the adapter.

You could theoretically use the TB3-to-2 adapter to connect a TB3/4 dock that offers downstream USB ports to your 2013 Mac Pro. However, for USB-C (USB) drives, simple USB-C to USB-A adapters would be a far cheaper way to go.

If the USB-C device is a storage device, link to it via a USB 3.0 to USB 3.1 adapter or cable. It will downstep to USB 3 speeds. Thunderbolt 2 can't be used on USB itself.