Getting a hub for my Dart...

My guess would be that someone pressed the studs out of the hubs at some time in the past without properly cutting the swedges, and hogged the holes out. After that, the stock studs will not fit tightly.

Like 4404spd said, take one of your studs to a parts store that has a Doman stud paper catalog and browse the pictures and specifications to find studs the right length and thread, with a little larger knurl diameter. You might be able to save that hub.

I, myself, in the past, have replaced the hubs, but that seems to be not so easy for you right now, so different studs may help.