OK, makes sense, would be 10 inch, and it matches pictures of others with that marking...
George's basement has a somewhat similar one, and thinks, based on the chuck, perhaps made by Millers Falls, tho your chuck isn't precicely identical.....(The knurling is different, but MF changed their knurlling rather a lot, you can probably date it by that...)
Georges' has cocobolo handles....
(Average ebay offer price is $8-$25 btw...)