These guides are made from a high tech, non-metallic composite material, "Graphite Impregnated Phenolic Laminate" which contains three synthetic dry lubricants that lubricate the blade but do not leave it oily. The metal to metal contact made by old metal guide blocks creates heat and friction which cause premature blade wear and breakage. These problems are eliminated with Cool Blocks® blade guides which allow blades to run cooler and last longer with less friction.