joint en caoutchouc qui assure l'étanchéité sur une tête de piston de frein

"Piston Cups are primarily used on piston heads, plungers or rams in hydraulic or pneumatic service. Its mechanical sealing surface is at its periphery.
Piston Cups are commonly used because of economical cost, excellent service life, efficient assemble, universal acceptance, and simple accessories.
Homogeneous Piston Cups are recommended to handle low pressures (under 150 psi) in air, water, hydraulic fluids, and lubricating oils. Homogeneous Piston Cups stocked by American Seal & Packing are 80 Durometer Nitrile. They are also available in other homogeneous materials such as EPR, fluorelastomer, and silicone."
http://www.pistoncups.com/



Fabric reinforced Piston Cups prevent extrusion in medium pressure installations (up to 1000 psi) or where diametrical clearances are greater.