This is Lego part #3960 4x4 Dish Inverted (Radar) with Solid Stud in Light Gray
NOTE: Light Gray is the correctly listed color for this part, not to be confused with the modern equivalent, Light Bluish Gray
Parts in this color and condition are considered New Old Stock. New Old Stock refers to parts long since out of production, but still in bulk in new condition. They can be considered Rare Parts, which you can find more of here
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