Altinator brushes SOM's

I am wondering if anyone has sucessfully sourced brushes for the smaller Lister Startomatics? I have found two places that will make them from my specification but as I do not know the correct grade of carbon/graphite composition due to the brushes being worn down past their markings am reluctant go ahead. The AC brushes are marked with a part number only.I have some big ones here that could be cut down to suit (making 3 out of one brush) but again do not know if their carbon composition is suitable For a SL1 1.75KW 230v set. Perhaps there is information somewhere on the grades that were used ?. Thanks. Chris.