i used to use dumbell handles like that but the collars used to constantly come unscrewed, mid set.
Thanks. That is a good point. With that much force and wide threads, they probably loosen easily, as you found.
I will likely get a cage or squat station later and an Olympic barbell. Right now I have a standard bar, with up to 160 pounds total, threaded dumbbells and a cheap bench (I have used this set-up for almost ten years.) For a better system, I wanted to go with a Hoist bench (cheaper makes online but I can not try them before buying and I hate taking the risk that I will not like them just to save $50) and dumbbells, then get squat stand or full cage later, if I want to do barbell stuff again (can use my old bench in mean time for barbell stuff.)
On powerblock and safety:
I called Powerblock. I asked if they ever had any reported injuries from the Powerblock coming undone. The lady said, no.
She said the four magnets would have to fail and the pin push out, past the range of the elastic tether before the weights would come undone (pin must be fully removed.) I agreed that I would likely notice that happening before it was too late.
She added that during bench presses, over head presses and pullovers, etc. (the exercises and points where I would be most worried - i.e. weight over my head) the powerblocks are upside down and even if the pins were physically removed the weights would not fall because of the upside down position of the blocks at those points.
Her answer makes sense??