How To Choose The Correct Core Plug
All core plugs are manufactured slightly oversize by 0.25mm – 0.40mm (0.010” -0.015”) which is the interference fit required to seal them snug in whatever opening they are being installed.
It is always best to have the original core plug to measure and compare when replacing. Although sometimes that is not always possible if the original has rusted away or been damaged beyond recognition. Digital micrometre is always preferred when measuring over a tape measure or rule where possible to get an accurate measurement.
If you cannot find the correct size for your application it is worth converting metric to imperial (or vice versa) to try and find the correct size. Please see the conversion chart.
Generally vintage and classic automotive vehicles will use imperial size core plugs whereas more modern automotive vehicles will use metric core plugs.
Same goes for core plug type, vintage and classic automotive vehicles will use dish type core plugs most often than not on the engine block. Whereas more modern automotive vehicles will use cup core plugs throughout the engine block and cylinder head.