Hi,

I have huge problem with those. Screws get stuck, spinning without unscrewing, can't fasten at all, and huge U bolt got stuck so we had to break it with huge pliers. Today I went to my supplier (Netiks, Belgrade, Serbia) and we tested few brand new pieces. All of them had similar problems.

Bad batch for Serbia or anyone else is having the same problem?

BR...

We have the same problem. Try to change the stainless steel nuts to a pure galvanized one.

Stainless on Stainless have a "gallinghttps://en.wikipedia.org/wiki/Galling" problem.
Greasing the nuts and limiting the applied torque tends to alleviate the problem.
There are "anti-seize" products designed for aluminum, that will also greatly help on stainless.