In reply to His dudeness, 3mm, which is about 1.5mm all round. This corresponds to the carburettors which are 30mm and 33 mm. For some reason on the 400 the internal diameter of the inlets tracts of the rubbers reduces to about 27mm at the cylinder head. I am guessing that it may be to restrict the maximum speed in the Japanese home market to 180kph.
In reply to Andrew, yes all the sprocket, generator, starter, clutch and cam covers are the same.
One of the changes I made to the my 2003 600 is to replace the sprocket cover with an early 600 one. This is exactly the same as the 400 one. It has a rubber damper and internal cover. The 2000 to 2003 do not have this damper and cover. It stops the sprocket nut from falling off if thesprocket nut threads frett which in turn stops the sprocket from falling onto the threads of the shaft which can damage the shaft beyond repair.