I may be getting one for very cheap, if I can, should I? I have never read up anything on them. http://www.hksusa.com/categories/?id=1940

 

I have some friends with RX7s running lots of boost with them. They're commonly used, long as there is nothing wrong with that one I see no reason not to get it.
I think they're bigger than the smaller sized 38mm tial so take that into account as well. If it will fit then go for it.

 

The guy selling it lists it as a 35mm, HKS says its a 40mm.. hmm