Z-Axis rod issues

Hello and good morning!

I have printed out all the parts to make a MPCNC and MP3DP.
Started assembly on the 3D printer first so that I could get it up and running more parts to start a MPLaser engraver. Everything so far has been going together quite well as far as hardware is concerned. However, the Z-axis has been giving me some issues. The threaded rod that came with the kit ordered here does not clamp well in the pineapple coupling (neither 5/16 or 8mm coupler) With the coupler fully clamped shut with the screws, there is still a very slight amount of play in the rod that causes it to sag; also, it is relatively easy to pull the rod out from the coupling.

I measured the rod with a micrometer and it measured out to be 0.290"-0.292". If it were a 5/16 or 8mm shouldn’t it be closer to 0.312"-0.315". If so I am about 0.020" off which would be enough to create a fair amount of play. However, I have been assured that my rod’s diameter is correct at 0.292"

I doubt it being an issue with my printer printing holes too large. Usually slicers have an issue with printing too small. Slicer is Simplify 3D

You bought that rod from me? It is still with in the right size range but I buy hundreds of them at a time and thread the nut on by hand if it was too small I think I would have noticed it. Maybe not. The pic below is from the batch I bought a few months ago, that I have been selling since.

Either way the coupler should still fit. If not there are a ton of parametric ones on everything just make one a bit smaller on the 5/16 end. I have to thread the rod in on the couplers I sell before I put a screw in there. They are very snug.