I read that the new cooling head was needed because the buttons were of different size. So I ordered the cooling head listed. !QUOT!I!QUOT! couldn't figure a way to make the cooling head work. So I ended up not using it, and just reusing the original setup. It works just fine. Again, !QUOT!I!QUOT! would say it's not needed, save your money. [:@] The only thing I needed to replace was the piston, sleeve, and connecting rod. I could have probably got by with the regular connecting rod. But I didn't want to take any chances and ordered the .18 size one. It's noticeably thicker than the stock connecting rod.