In order to to help keep the heat out of your carburettor. Available in 22, 24, 26, 28, 29, 30 and 32mm sizes (3mm thick) to suite the AMAL Concentric 600 and 900 series and the AMAL 375, 376 and 389 Monobloc carburettors as well as other applications where a 2" stud spacing is used.
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