he guy, Iam also looking to up grade my shift knob, i did some research and found that the thread on the mazda's are M10 P1.25. good luck with your choose.
http://www.optionimports.com/arctishknro1.html this is where i found it.
for those of you that don't know where to buy it (like me), go to the eibach
web site, and click dealer location. then go down to buy online. they're gonna give u a list of other sites. I took the time to look at all the sites, and only auto anything shopping and auto accessories garage had...