FAL, gas regulator

Type A is typical of Israeli and early FN short gas plug /long gas tube models, and rotates multiple times for adjustment.
Type B is open to close in one rotation and utilizes a flange on the left handguard to prevent over-rotation
Type C is open to close in one rotation and incorporates a tab to prevent over-rotation (most common).
Type B and C are functionally interchangeable.
VG-EXC