One more thing I have installed many WSM pistons,I have never seen a piston related failure in one of them,years ago maybe but not in the last 6 or 7 years.On stock or lightly modded applications they work fine as does PROX,SUDCO,OEM or any other piston.They hold tight mfg tolerences as far as sizing and seem to be made as well as oem pistons.They also use RK rings which is what PROX uses as well.If you are building a high dollar race or rec engine then I reccomend you use use high dollar pistons,in that application I use WISECO which work fine as well as long a proper piston to wall clearances are used.