Looks like a air valve cap from a bycycle tire to me.
Could they be an old style of Marette (sp?) The caps you use to twist household wiring together.
These buttons are way too small to be a tire valve.
I'm telling you, I'll bet you anything they are a vintage on/off twist switch.
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Aren't one of these found on the one of the gauntlets as well, maybe it was functional (not the ones on the helmet of course).
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