The sector gear is the gear that directly engages the piston, and is the final step in creating the amount of torque necessary to pull back the spring. It has a large, and clearly defined rack of the teeth that engage the piston, and a small rack on the underside that engage the spur gear. It also has a small nub on the inside of the first, larger rack that engages the tappet plate and allows it to function. There is also a small egg-shaped nub on the underside of the sector gear, which engages the cut-off lever, which is necessary to retain proper semi-auto function.
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=== IIj. The Anti-Reversal Latch: ===