They're made out of aluminum. I've broken 3 plastic rod holders and lost 1 spendy custom rod and reel to the sea. That's why I built these. They're solid and with the clamping features that I have on them they will take a lot more force than the plastic ones will before rotating on the rail.
I know what you mean. I lost a nice net out of Newport. I had it in a plastic rod holder up forward just a bit. I look up for the net and only saw an upside down rod holder. I dont use the rail hoder any more.