Adjustable design for a wide head size The knob on the back lets you quickly adjust the fit. Suitable for head circumference 20.5 to 26.0 inches. The foldable mask and goggles can be sized via the elastic band on the back wall. One size fits most. FAST SF helmet features Adjustable Head Locking Strap Suspension System with size control by the knob. Includes rail, VAS Shroud, loop patch, and anti impact EPP cushion. Compatible with Picatinny adapter, Goggles Swivel Clips, and NVG Mount Adapter. Headset belt groove ensures secure placement of a headset. Tactical goggles Main body made of nylon for strength and wear resistance, staying stable during activity. Natural face fit, breathable, comfortable, wear resistant and impact resistant. Ergonomically designed to provide a full range of vision. Multi functional balaclava fabric, soft and breathable. Can be used with the airsoft mask in tactical games, and also as scarves, hats, neck tights, outdoor riding, etc.