WorldPac (Pack of 4) E Track Fitting with 6.5mm O-Ring - Single Plated Based (Pack of 4) O Ring fitting to fit on all standard E-Track Single Plate Base with 3,500 LBs Capcity 6.5mm Thick O Ring with 2.5" Diameter Ring 5/32" thick plate held together with single 3/16" rivets Zinc Plated Gold Chromate Finish Base for Corrosion Resistance