I forgot to mention that Guy's unit uses a stock shaft, in fact, you could send him a core. Pretty sure thats what I did. I have both kinds. I loaned the HPM's to a friend when his stocker blew up earlier this summer, and I have been running the Emerald for a year or two, now. I even forget the prices, now, but I'm pretty sure both are cheaper than stock. I like HPM's because he is good guy, American business, inmate here, etc and not least he does world class work.