These inserts roll into the extrusion profiles and keep the T-nuts from moving around. It suck when you're installing the enclosure and have to remove it again because the T-nuts slide out of reach. Only works for a specific type of nut. 

Print in PETG, PLA deforms too quickly from heat and the model is quick to warp when using ABS/ASA. Thread holes with an M5 tap (or use a ground down M5 screw) and install M5 set screws. These need to be 6 to 8mm long, 4mm also works but 10mm is too long. Slide the inserts in the frame and loosely tighten the set screws. You don't need to tighten them all the way, there's a little bit of play allowed. Observe the correct orientation for the T-nuts.

You'll need to print:

• 2x tnut_spacer_side-A
• 4x tnut_spacer_side-B
• 2x tnut_spacer_side-C
• 2x tnut_spacer_top-A
• 2x tnut_spacer_top-B
• 1x tnut_spacer_top-C