This is a simple open case designed to be used with the Black Magic Probe v2.1 by 1BitSquared. (https://1bitsquared.com/products/black-magic-probe
). This version of the case has fins for extra protection of the JTAG connector.
There are small tabs that hold the corners of the circuit board in place. Tilt the board and insert the USB-connector end of the board into the shallow end of the case first. Then slide the other end down, spread the sides of the case apart as needed until the board snaps in place under the tabs. Of course, be extremely careful not to put pressure on any components on the board!