Brian runs an external Thunderbolt 2 drive and Parallels to dual boot into Windows. He upgraded his SSD, which works on his laptop, but it won't attach to his Mac Mini. How can he adapt it? Leo says that the Thunderbolt 3 connector is the same as the USB-C connector. But that doesn't mean it has the Thunderbolt controller built in. So he may need to get a Thunderbolt 3 external enclosure to use it, but it's not cheap. He could use a Type A USB 3.1 data cable connector to the Type-C drive and he should get full throughput. The chatroom suggests this SanDisk Ultra Dual Drive USB Type-C.
But it won't be Thunderbolt 3 speed.