W9 is 7/16" Coarse....... You have to use the appropriate brand for the appropriate stand, ie. T&D stand bolts will not fit on a Jesel stand. (too tall of bolt head)

ARP just supplies Jesel/T&D with bolts, they have no idea what they are using them for, so no they would not know which bolts are correct & most likely have a proprietary deal with each company that you can not buy their rocker stand hardware through them (must buy direct form Jesel or T&D etc)