These wide rubber rails are designed to channel water along the surface of the blade eliminating the "slipping" effect when kicking, and to protect the edge of the blade against impact. The grade of rubber was chosen for the correct ratio of stiffness and flexibility, allowing the rail to flex with the blade, while maintainng enough rigidity to channel water. These rails can be installed on any fiberglass or carbon blade.

If you're replacing old worn out rails you will need to scrape them off using a utility knife or a stiff razor. When scraping off the old rubber do not be overly concerned about damaging the blade, just confine the scraping to the area that the rubber rails will cover. The surface of the blade should be free of old rubber and glue residue. Cutting a little into the resin of the fiberglass or carbon blade will not cause a problem. A Cyanoacrylate glue such as krazy glue is used to permanently bond the new rails to the blade. For best results use a Q-tip dipped in acetone to clean the groove of the rail where the blade will fit. 5ft will be enough to do two blades of conventional length such as the Speardiver C90. Measure your old rails to be sure. Rails can be easily cut to correct length with scissors.

See this link for a good explanation of the different kinds of rails, and what makes some better than others Fin blade rails, water channeling and tendon rails explanation