You are buying 1 aluminum gear with 40 tooth. Mates with 8 tooth bronze gear
perfectly. Ideal for use with gear assemblies when plastic gears are too weak
and strip or break. Comes with remove stainless steel shaft that
coincidentally mates with XL motors. Gear assemblies can be made out of plastic
beams and standard motors, or made with aluminum beams for use with even higher
torque. Use in physics experiments or scaled moc-ups to do real world tasks.
Adding metal to construction requires adult supervision, because they can
generate up to 200 times more torque, where plastic gears break down.