[lurkingknight]

you can still visually check them if you rest them on a flat surface. You'll also notice the channel where the tappet locks into is also cut more forward or rearwards depending on brand, and even batch sometimes (shs 14th tooth piston anyone?) if you look closely enough. just a tiny difference like that can move the tip of from nozzle to nozzle to cause a leak or misfeed when you combine it with any other number of manufacturing factors in airsoft. I make it standard practice to measure every single part that comes out of a gun now.. from gear tooth thickness to bore diameter of nozzles.

I'm not talking thousandths of a mm here, I'm talking hundredths and sometimes even tenths of a mm difference.