The guide rings type Aston Seals FSP have been realized to substitute traditional bronze guide in hydraulic cylinders. They guide the rod of a plunger cylinder where, thanks to the big longitudinal grooves on the outside surface, an overflow of the fluid is continuously assured. The compound used for these guides is a medium viscosity acetal resin glass fibre reinforced characterized by high strength, rigidity, hardness, impact resistance, resilience and excellent stability to high and low temperature.