genius F-1000 fight stick mod help

hell guys, i am an old reader of srk forum. but this is my 1st time posting anything. i tried to search the forum but couldn't find anything on this stick. so , yeah i am really new into this. and i want some help with some pretty stupid stuff. can you guys tell me what size button this stick has. this is the only stick available in my country ( bangladesh ), i just brought it. i was thinking of buying some sanwa parts from abroad. a bit confused about the button size.
http://www.geniusnet.com/wSite/ct?xItem=56629&ctNode=164