Front eyelet grommet for attaching an insignia,regards minnie.
This is your standard WWII era M1 liner as can be determined by the khaki colored webbing. This liner may or may not have been recycled for use in Korea, too. It's salty, but looks to be all there with intact leather chinstrap and sweat band.
The grommet hole at the front of the liner was used to attach rank insignia.
Hard to tell from the picture so I could be wrong, but it looks like it has green painted “A” washers holding the webbing which would date it as mid war period. It also looks like it has green rivets and buckle on the chin strap which also comes from mid war to slightly earlier.
The number below the Westinghouse logo is believed to be just a mould number so they could tell which mould a liner came from if a fault in the manufacture developed. I ask this question as well when I started.