The gas mask is in fantastic condition. It appears that it is a size 2 (medium) and the code byd indicates it was manufactured by Drägerwerk, Heinr. u. Bernh. Dräger, Gasschutzgeräte, Lübeck, Schles.-Holstein.
The partially visible WaA code on the mask is 533, this was the factories assigned inspection stamp number.

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Regards
John

"It is always wise to look ahead, but difficult to look further than you can see" - Winston Churchill