If you are printing a Z-brace mod (like this one https://www.thingiverse.com/thing:921948/#files) but you were only able to source 1/4 inch rods and nuts, then you may find that your printed knobs are too big to grip the nuts.

Print these inserts in PLA (should only take ~3 min. each). Drop each insert in boiling water to soften up, if you have to, before squeezing the nut into the insert. Then you can pop the nut and insert into the 3d-printed Z-brace knob without any issues!