7 metal teeth half rack 14 teeth piston

Great for 1j low stress high speed builds, especially if you're new to building aegs and want to experiment. Very beginner friendly.

Plastic rack in the back gets torn out if the replica prematurely engages whether its from a bb jam or you messed up your gear timings. You want that to happen so it will save your gear set rather than metal rack on metal gears causing torn gear teeth on the spur and bevel. 

7 metal teeth at the front is perfect for precocking because precocking plastic gears will wear out over time. Having 7 metal teeth allows precocking while still having an intentional failure point with the plastic teeth at the back if a malfunction were to happen.