A new design for the Prusa I3 Mk3 feet, aimed to be printed in flex and to reduce vibrations. They have a greater contact surface than the original feet, and the design spreads the stress of the corners throughout all the foot. Using different thicknesses (the full perimeters and a somewhat sparse gyroid infill) helps to spread and absorb the forces. The feet base is just slightly taller than the original feet; is also round (15mm dia.), so additional hemispheres can be installed.

The suggested way of printing & installing:

• Print some pairs of prusa_Mk3_foot_A.stl and prusa_Mk3_foot_B.stl (see details below; use gyroid infill!). 2 pairs may be enough, but go for 5 pairs for overkill points.
• Print also some 3030 t-nuts, 3030_t_nut_nosupports.stl
• Prepare some M3x12 (or M3x14) countersunk screws, and M3 nyloc nuts. Maybe you still have them in your kit "Spares" bag…
• Insert the nuts into the plastic t-nuts. Use an M3x10 cap screw to fully insert the nut if needed. Check the nuts work properly on one of the side channels of the extrusions.
• Connect the printer, autohome, and move Z axis somewhere up and X axis full right.
• Turn off the printer, unplug it, turn it over the PSU side and install the feet. Alternate the pairs (see the cutting mat picture), so the forces balance. Do not overtighten, the steel screws may bite the aluminum extrusion. Just tighten enough so the feet don't quite move, leave fixing to gravity.
• Put the printer upright, plug it, connect it and enjoy!

For additional overengineering points, you might want the first layer of gyroid infill to be parallel with the extrusions. In your slicer, note if this first gyroid infill is either parallel or perpendicular to the base (circle) linear top infill, and install accordingly.

It's good to give the base (circle) of the feet a slight sanding (180 grit is okay) for improved adhesion. For overkill points, use 10 feet (5 pairs), alternating them as instructed, and concentrating them around the gravity center of your Prusa (which is about the frame). 2 feet at the start of the short extrusions, and 2 more at the start of the long extrusions, work nicely. Beware of the wiring and loose Allen keys!

If everything goes OK, you'll notice (like I did) that the rattling in gap fill and high-speed gyroid infill is almost if not completely gone, and that your Prusa "sings" in a deeper voice —meaning the higher frequencies are absorbed!

Some variations:

• A "mixed" feet model is included (prusa_Mk3_foot_AB.stl), which is like both feet joined. This does not need alternating, and I'm not quite fond of it, but YMMV.
• If you like threading plastic, there's also a 3030_t_nut_selfthread.stl file, without room for the nyloc nut. Again, I prefer metal and nylon to just metal or just plastic, but tapping-lovers, be my guests.