This is a locking collar for a standard barbell. I printed everything 30% infill with ABS. I didn't get a chance to print with flex, but I would like to include a piece for that. Currently I just cut some rubber and glued it to the center side spacers so that the collar will grip the bar. They work great. You may have to download the stl and modify the "side_grip" piece and add or take away some meat based on the thickness of rubber you find.
You will need 4 #6-32 12mm long flat head screws to complete the build as well.