This is Lego part #4477 1x10 Plate 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

We also have many non-production Lego parts available for purchase, click here to view them all.