Corroded screws on Kessil - Do these contain Tin?

[TexasReefer82]

I've been battling high Tin in my tank lately and have been trying to eliminate all potential sources. I've already found and removed two corroding metal items that were likely sources. An additional potential source is a Kessil A80 fixture that hangs above my refugium in the sump. Over time it was inevitably subjected to salt spray and the screws on the bottom appear to have some corrosion. Does anyone know if these screws used by Kessil contain Tin???

 

[TexasReefer82]

Another possibility is this mounting bracket which comes with the A80. The screws attaching this bracket to the wood mount are obviously corroded and they will be addressed. I'm wondering about the bracket itself.