Summary

Top and bottom fit together. Bottom securely holds the 9 volt battery. You will need some 3mm nuts and bolts. I used nylon. There's a rectangular hole the width of a three-wide female header. Adding the female header is optional, it does not add any functionality it's just a nice to have. If you use it, bend the female header pins 90 degrees and solder directly to the board under the hole. You can always do this later. Pin number callouts are included in the design, but make sure they are right for your board.

My board says:
LCR-T4-H
M-Tester V2.68