15mm OD This rubber plug snaps into early master cylinders to allow the brake fluid reservoir feed pipe the proper seal into the cylinder. Most original plugs are cracked and leaking. Fits into our replacement Master Cylinder part number 113-611-021C. 17.50mm OD 4.5mm ID Fits in Master Cylinders with a bore OD of 15mm Beetle Type 1: 46-66 Ghia: 56-66 Quantity: Sold EachMaster Cylinder Plug Fits Type 1 Beetle 46-66 Sold Each