Note: I had to select a specific model to upload this, so it shows I'm using an anycubic Kossel, but I'm using an anycubic Kobra Max that wasn't on that list
PETG works great for this, but I used ABS. PLA WILL NOT WORK FOR A 3D PRINTER ENCLOSURE, the melting point of PLA is too low for what you would need to run in an enclosure and the PLA would be exposed to lots of moisture due to the heat variances and condensation.

The corner bracket is 2 " x 2" x 2" x 1/8" thick, and the edge bracket is 3"L x 1"W x 1"H x 1/8" thick. The holes are .2" (close to 5mm). The holes intended use are for 7/32" aluminum rivets, but most people will probably end up using bolts (you can always drill the holes out if needed). Eventually I will upload multiple brackets labeled with different sized holes, but for now I'll just upload what I have.

After hours upon hours of searching for some brackets for my 3D printing enclosure, I was not too happy with anything I found, most brackets were outside fit, which I didn't like, and most were too brittle, thin, and/or too small. So I hopped on fusion 360 and designed up what I thought would be a good, strong bracket.

The corner brackets have a unique gusset on the inner edges to proved extra strength, and a rounded look for aesthetics. (I will upload pics of my full enclosure once everything is fully assembled, I have to remove the original, half broken PETG brackets that I printed from another users design.

The edge brackets have three beefy gussets, as well as an inner edge gusset identical to the corner bracket. I tried to break both brackets with my bare hands, and succeeded with the corner brackets due to its size and therefore increased leverage on the bracket, but I could not break the edge bracket with all of my strength with my bare hands.

Anycubic

Kossel

No

No

.15mm

20%

ABS is not necessary, I used PETG for my enclosure originally, but they weren't as strong as I would've liked them to be.