New rear wheel cylinder for your rear drum brakes. 5/8" bore. Fits original-style 1968-1974 Opel rear brake systems. A required safety upgrade, particularly on a long-stored Opel. 2 required per car. (For best results, we recommend installation with our other new rear brake system components, including all-new higher-quality brake shoes, hardware kit - and on the GT, a new parking brake cable).