it is obvious that you have not ever used one,,,the seater stem must be used from the original seater top,,,if it is a 30 cal seater you use the 30 cal stem with your new micro seater top,,,then that top can be used with other 30 cal dies (308-30-06 etc,,) if you want to use it on a 6mm or some other cal you must remove the 30 cal stem and install the appropriate cal specific stem,,,,,,I try to have one for all the cals that I commonly reload for,,,,I like the Siclair top better because it has more travel (adjustment range) and does not have the lip that over hangs the body of the die,,,the Sinclair has .050" travel per rev on the adj top whereas the Wilson has .025" ,,,,it is easier for my feeble mind to do the math with "50" thou per turn,,,and I like the adj for tension that holds the set points in place on the Sinclair,,,,(the Sinclair costs 5 $$ more ,,,but worth it !!),,,,just my .02 $$....Roger