This is just one of the filler pieces to cover some of the holes on a printed solid enclosure. Double side tape not required but recommended. one is for thicker tape (2mm) and the other is for thinner or no tape.
Assembly steps

1. Print 2
2. Tap the smaller non-chamfered holes with an 8-32 tap.(or just force the screw.)
3. Assemble pieces as shown
   Note- May require sanding of the slot especially at the joint.

LulzBot

TAZ 6

.2mm

20%

I printed with the top end down to save on support material. but it could be printed the other way.