Usually, the black rubber that fits into the molding is one complete piece that starts at the stern and butts up at the stern. I think that D & R Marine sells it in 60' lengths but he may have pieces of it at his store that he could sell to you. http://www.drmarine.com/categories.asp Give him a call.
thankyou for replying. I'm short 2 feet of the insert on a repair and can only find full lengths. Unfortionaly I'v throwen away leftovers in the past and hoped someone had 2 feet to sell. New or used will work
I am replacing all of my Rub Rail and that includes the Rubber insert, I have 50+ feet of the old insert, (its not in bad shape) and I will probably have some left of the new stuff when I'm done replacing mine. Does this help you? Let me know, like I said the old insert I took out is in good shape, the only reason I'm replacing it is becasue the PVC Rail that holds it is an Eyesore.