Do a Google search for "Trident Rod Holder"

I see some are aluminum. Mine are Stainless.

There are double set of grooves in the pipe that slides into the gunnel rod holder on mine so they can be rotated every 90 degrees to run of the back or the side. They work great for me.

I built a Big John adjustable single holder to run off the rear gunnel with a Dipsey. So I can run 3 rods off each big board and a single rod on each side with a Dipsey keeping the spacing better than 4 rods off a big board on each side.

Hope this helps.