With the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter you can connect Thunderbolt and Thunderbolt 2 devices, e.g. external hard drives and Thunderbolt docks, to the Thunderbolt 3 (USB-C) / USB 4 ports of your Mac. It's bi-directional, so you can also use it to connect new Thunderbolt 3 devices to a Mac with a Thunderbolt or Thunderbolt 2 port and macOS Sierra or later.
You can also use it to connect a Thunderbolt display, such as the Apple Thunderbolt Display and LG Thunderbolt 2 displays, to the Thunderbolt 3 (USB-C) / USB 4 ports on your Mac. However, if you use it with an Apple Thunderbolt Display, a power source is required, as the display does not transmit power through the adapter.
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