As the standard knobs of the bed of the CraftBot tend to loosen, here some versions of that knobs, based on a M4 Lock nut. The lock nut has to be pushed into the knob. It's very hard to twist / mount them because of the resistance of the lock-nut. But they won't loosen anymore ;-)

When replacing the three knobs, be sure to keep the 'hat shaped' spacer in the build plate, as without it the plate will move while printing. There is one version of the knobs to replace that spacer as well BTW. I recommend the "knob bed CraftBot higher" to use. Print it with PLA and solid. No need for support.