This is a set Anti-Wobble Brackets. Their purpose is to isolate the wobble of the threaded Z Axis Rods to improve the print quality. They are designed to replace the factory nuts on the Geeetech Aluminum Prusa I3 that came with stamped steel Z Brackets.
2 standard M8 Nuts available at most Hardware Stores are required. It should be sized correctly, but if the brackets are tight on the smooth Z Rods, some shaving or sanding will be required to allow smooth movement so they will not jam causing lost steps.
Supports are recommended for the area where the nut fits.
Please check out my video: https://youtu.be/mYswkbC_AX0
This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/lhubjMRleuR