Do you mean the rubber insert, or the aluminum rail, or both? I think you’ll find info here by searching for “Wefco,” the company that makes rubber inserts. Not exactly a household brand!
This isn’t responsive to your question, but I gave up on mine last year. The rubber looked terrible, and keeping the corroded aluminum painted was futile. It was also detaching from the side of the boat in spots, and the thought of repairing that and reattaching the hideous components was depressing. I replaced both sides with long strips of routed PVC lumber called Versatex. 2x6 - 18’, cut in half lengthwise, channeled with a dado blade on a circular saw, and rounded on the edges with a router. There was some fussing to shape the forward and aft ends to fit into the rail caps, and only one joint on each side since the material was 18’ long. Versatex is easy to work with, UV stable and cleans nicely with Softscrub. Its only drawback I’ve noted is that like all PVC, the dust it throws off from sanding or sawing is very sticky.
(We also painted the topsides last year, with Perfection, and I slapped the checkerboard sticker on at the last minute rather than splashing the boat without a colored upper stripe. It’s a reflective tape from eBay. I’m pretty sure I really like it although it is not traditional Ericson dressage.j