1-3/8 inch Bore: Lower operating pressure than standard 1 inch bore units2 inch Reserve Tube: More fluid for more consistent performance5/8 inch Piston Rod: Heavy-duty nitro carburized rod for long service life. On non-dust shield units onlyThe Monroe Gas-Magnum truck shock absorber is designed for mid to full size, hard working pick-up trucks and vans. These units provide firm control without a harsh ride. With up to twice the fluid capacity of standard 1 inch bore shocks, Monroe Gas-Magnum truck shocks work more efficiently with less effort.