Size of Platform to Bed adapter bushings

So the size of all the various bolt and screws are right on their bags, but I’ve had an issue where one of the platform to bed adapter bushings did not have really clean threads and one of the M4x10 Flat Head screws got jammed into it. I was able to get it apart, but not without removing the whole bed again. Then I chased it out with a 4MMx0.7 tap to clean the threads. Did the same with all the other ones that were ‘sticky’.
My question is, what is the size thread in the Platform? The back side of those adapters. This way I can order some stand by replacements from McMaster-Carr or equivalent