Reed & Barton Francis I Silverplate Wine Stopper mint in box #1524

Description

Hello.  We are original buyer of this wine bottle corn stopper:  Reed & Barton Francis I pattern.
Original box and small plastic bag come with stopper.  We bought this, put it safely into a drawer, and it's never been used.  It's truly "mint in box" condition.  Please see photos posted here.
The stopper is used on the cork for a bottle of wine.  Stopper weighs 2.2 ounces and feels like sterling but I can't find a sterling mark.  On the underside of the stopper, the name Reed & Barton is etched into the item along with number 1524.
If you're reading this description and know whether it's silver-plate or sterling, please advise me.
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We have  other Francis I items up for sale now ebay so please check them out.  Thanks!