An original BSA standard 8 inch half width Hub / Drum assembly part number 66-5556 used but in good condition ( Has internals bearings / spacers etc ) suitable for BSA M20 500cc Side Valve Single.BSA M21 600cc Side Valve Single.BSA M33 500cc OHV Single.BSA B33 500cc OHV Single.BSA A7 500cc OHV Twin.BSA A10 650cc OHV Twin 1950 onwards.