bbs caps

Hi guys I'm new to this and probably got the wrong part. In need of some help. Iv got some bbs deep dish wheels. I can't find the hexagon threaded screw in bbs  caps from any were, are they hard to find or am looking in the wrong place. Can't put any pictures on because I am new. Would love some help plz

http://www.the-polisher.com/id31.html