this is a brace for delta printer which uses 2020 aluminum profile.
This design origins from this link http://www.thingiverse.com/thing:626279
He has uploaded 1515 size only. so I made it myself for 2020 size.
There are two version. one is for 4mm nut and the other is for 5mm nut. check the file name.
good luck with your 3d printer.
I have added 123d source file in case old design not fitting your 3d delta printer.