These are mounting bracket for Anet A8 and A6 printers. Their purpose is to hold down and stabilize the printer base so it doesn't flex while printing or come out of alignment when moved.
Print four brackets, one to hold down each end of the threaded rods as shown in photo. IMPORTANT: To work correctly the brackets need to hold the printer tightly to the mounting surface, so be sure to put a small piece of duct tape on the inside of the bracket to provide a tighter grip against the threaded rods and prevent slipping.
For best results the printer should be mounted to a rigid stable surface. A sheet of 3/4 inch or 19mm particle board, mdf or plywood should work well. Be sure to use a good quality material, especially for plywood, so it doesn't warp. If you don't need portability you can mount it directly to a sturdy table or work bench. Three files are included:
hold_down_bracket.stl - This is the original version and is designed to fit the Anet A8. I've had the same set of these on an A8 printer for two years now and they're still going strong.
hold_down_bracket_a6.stl - DO NOT USE. This is the first version for the A6, it was designed based on comments and feedback, and is for historical purposes only. Use the updated version 2 for the A6.
Hold Down Bracket A6 -v2.stl - Updated version 2 for the A6. This one is modified from the original, based on comments and feedback. Note that I do not have an A6 to test this, so please let me know how it works.