This is the core plug, also commonly known as a Welch plug, specifically for the Cooper S A-Series engine block. This is a 1-5/8" (41.4mm) cup-type brass core plug and is the correct size for the Cooper S block. FEATURES Cup-type brass core plug Diameter: 1-5/8" / 41.4mm Specifically for Cooper S A-Series blocks 4 required per Cooper S block Brass construction provides excellent corrosion resistance IMPORTANT – CHECK YOUR ENGINE BLOCK These core plugs are different from the standard 1275 A-Series block plugs: Cooper S: 1-5/8" / 41.4mm – cup-type brass plug AEC876: 1275cc non-Cooper S block – 33.6mm cup-type plug 2K8169: Small-bore A-Series – 1-5/8" / 41.4mm convex-type plug Although the 2K8169 is the same diameter as the Cooper S core plug, it is a different style of plug. Please check your engine block and existing core plug type before ordering.