Here I have a 1/2" drive gearbox sprocket nut socket ,its extra long so you don't have to remove the gearbox mainshaft to remove the sprocket nut, its 38mm ( 1 inch and 1/2" ) across the flats, It will fit the Bsa C15/C25/B25/B40/B44/B50 and Triumph T25,as well as the triumph T100/ T90 unit engine . It will fit other models, Matchless and Norton gearboxes have the same size sprocket nut 38mm across the flats, Overseas p/p is a estimate ,please ask first. The socket could be painted red or black depends on which paint I have to hand !