Fibre-Metal® Nary® F300 Headgear with 3" crown ratchet headband accommodates 8" X 11 1/2" 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.