The G&P White Polycarb Piston is very light and very strong. Polycarb pistons are great for keeping a lightweight power train that won't damage the gearbox shell, but at the same time remain strong enough to hold up with mild upgrades. G&P designed this piston to be used with upgraded springs which is why they gave this piston 3 metal teeth. This piston is recommended for use with mildly upgraded guns.
The use of aftermarket airsoft parts is not an exact science. Some parts may require fitting even thought they were designed to fit without modification. Professional installation of upgrade parts is highly recommended.