One dumbbell bar appears to be defective. None of the collars will screw onto that bar despite working on the other dumbbell bar and straight bar.
Amazon can't/won't do a single part replacement, so I'll have to ship the whole 100 lbs back to them.
I will update when the second set arrives.
Update:
It was too much trouble to figure out how to repack all the weights since Amazon offered a partial refund of 20%. I'll just use that refund to purchase another dumbbell bar or two.
The bars themselves feel solid. The straight bar comes as two pieces with a central collar that you screw both pieces onto. About two inches of threading per piece go into that collar. I'm assuming it can handle the 85 pounds of weight that comes with the set. The straight bar + central collar + 2 collars on each side is 13.5 pounds.
The weights are a plastic covering over something that I can only describe as feeling crunchy. I suppose I should avoid dropping them on the floor. Oh well, ## pounds is ## pounds. I didn't have to spend even a hundred dollars on this set so it's worth it to have some weights at home for days where I miss out on the gym.