1/2 inch Diameter Piston Rod: Nitro carburized rod for long service life. On non-dust shield units only1-3/16 inch Bore: Larger bore than most shocks to provide more efficient and consistent controlAll Weather Fluid: Contains special modifiers to reduce friction and ensure smooth rod reactionMonro-Matic Plus shock absorbers are nitrogen gas charged and feature velocity sensitive valving and all weather fluid, which offers passenger cars improved comfort at an economical price.