Looking at the detail drawings of the regular, extra and 420SS there is a variance in diameters on a couple thousandths that would effect how easy they go in.
Of course the hole they go into is not getting smaller either.

They seem to have a .010 tolerance on dia.. Maybe changes in manufacture etc. would end up with different diameters and .010 would surely make a difference in press fit. ..:beerchug:

You guys are making it really hard to decide what to order.:biggrin2:

My guess is that either will work ..so just flip a coin.

http://www.sethmad.com/wp-content/up...oinFlipPSD.gif

Order both then you can't go wrong :beerchug: