This helmet features the lightweight durability of a thermoplastic shell with Small Window viewing area, with helmet flip up operation. The Model 911P offers a horizontally positioned 2" x 4 1/4" lens with an aluminum front and our patented Zahnlok headgear.  Huntsman patented Zahnlok adjustment system allows the wearer to adjust the headgear in 1/16" increments to exact head size, simply by turning a knob.  The adjustment is automatically locked in with 50 meshing teeth to ensure a snug, comfortable fit that wont slip.  The system is durable and long lasting, because the teeth are automatically disengaged while the headgear is being adjusted.