On my Prusa MK2S, I had installed a Y belt tensioner that allowed me to easily adjust the tightness of the Y belt. When I installed the Prusa Bear upgrade, I needed a new way of doing this.
Searching around, I found what looked like a nice setup for the MK3. This did not fit the Bear frame so I re-designed to to work.
The redesigned piece mounts upside down compared to the original. I also made a modification to the space reserved for the idler pully. The object I remixed from had a few versions depending upon what type of idler pulley you have. As I have a toothed 20T pully, I downloaded that version.
I decided that I didn't like the way the pulley could touch the sides so I enlarged the opening and left enough room for the pulley and two 3mm flat washers. The opening is now 10mm wide.
You can refer to the original part for some more details about the hardware required. I used a 25mm bolt for the tension adjuster, yours could need something slightly different depending upon the length of your belt. In the original piece, there was a nyloc nut inserted into the adjusting arm. Since I can't get behind the fixed piece, I moved the nut to the back of the main bracket. The adjusting bolt goes through the arm and into the fixed piece. The adjustment range is somewhat more restricted than the original but there's more than enough adjustment available.
I did find that my original belt was slightly too short so I replaced it.
Probably doesn't need 100% infill but why not? I included a small bit of built in support for the hex hole in the bracket. This is probably not needed but may help.
I printed this using eSun PETG.