I am trying to mate threads of a nut and bolt such that there is no interference between the two for a FEA simulation.

I have made my own nut and bolt as well have taken existing models from McMaster Carr and the Solidworks Tool box.

I have tried coincident mating the nut and bolt and then screw mating them. Still with these mates there is interference and occasionally Possible Interference

As an additional question, what does it mean when there is a possible interference?