The main housing of the Madbull XF piston is Nylon polymer with a fiber reinforced structure (to better hold out against lateral forces, like violently spinning gears for example). The first seven teeth are steel (heat treated for strength) to engage the initial force of a spinning gear on the resting piston and then the remaining eight teeth are polymer (as the remainder do not need as much strength and the reduce wear of polymer is preferred where ever possible.).
The Madbull XP piston is available in full teeth and half teeth versions; the full teeth is used with normal gears where as half teeth are for use with helical gears.
Also, on certain kinds of high torque and super high torque gear sets the lower level of teeth on the sector gear (which engage the spur gear) can be high enough to engage the piston. In this case, a half-teeth piston is required to ensure contact is made only with the outer sector teeth and not the lower teeth.
Please note that this is just a piston; this piston does not come with a piston head or cylinder.