Piston

Gear teeth along the piston's top engage the gearbox's sector gear, which pulls it back against the spring during cocking; once the sector gear's teeth run out, the spring drives the piston forward on its own, its head compressing air in the cylinder ahead of it.

Piston material and tooth count matter more than they look: a full metal-tooth piston handles higher spring weights without stripping, but adds mass that can slow cycle speed, while a partial-tooth or polymer piston with reinforced teeth balances weight against durability. Piston damage — cracked teeth, a broken head — is one of the most common gearbox failures under a heavier-than-stock spring.

Full-metal-tooth pistons have a reputation for being noisier and marginally slower than polymer ones with reinforced teeth, so many tuners choose the reinforced-polymer option specifically for lighter, quieter, still-durable builds under moderate spring weights.