These are support brackets lasercut from 2mm thick aluminium that will help prevent the buildplatform from sagging and vibrating which cause quality issues on prints.

They fit snuggly, just replace the original screws on the side of the plastic arms with longer screws. I could only find M3x30 which are a little too long so that´s why i have included a spacer.

Obviously you need to have access to a lasercutter or punching machine to make the brackets.