This is a Anet A8 frame brace for(if your looking at the front) the right side.
This is to help stiffen and give support to the X axis. I also believe it helps with the Y also.
Here are the details of the print:
Material: PLA - Any material is just fine
Layer height: There is no need for super fine resolution. The print in the picture was 0.28mm
Bed Temp: 40C with Blue Tape
Nozzle Temp: (please adjust to your chosen material) 230C PLA
Print Speed- 30mmps
the Top plate must be removed, install brace then reinstall. I designed to have a nice snug fit to eliminate any chance of wobble.