Carl Swann, who gave this to me <thank you, again!>, said this copper alloy letter opener belonged to his grandfather.  It’s 8 inches long, slightly over 1 inch wide at the handle end, weighs 23 grams and is a little over 1 mm thick (that’s inconsistent, but I didn’t want to go to all the trouble of spelling “millimeter”).

Copper letter openers are still top-drawer specialty items today, but I think this was early B&E, maybe mid-30s.