Fibre-Metal F300 Headgear with 3 inches crown ratchet headband accommodates 8 inches X 11 1/2 inches windows and suits easily into spectacles with space for air circulation to avoid fogging. This free floating headgear resists heat and features a slot/pin mechanism with locking cams. The channel grip system mounts windows and grips them in place in a deep recessed channel to secure from dirt and debris.