The German researchers Pape & Kellner in their monumental directory of Gun Makers has two listings for Hollstein (Holstein) in Helmstadt. They are-
Heinrich Hollstein– gun maker and gun dealer at Langesteinweg 14 in Helmstadt circa 1904 to 1928.
Hollstein & Löhr- Wilhelm Hollstein- gun maker in Helmstadt circa 1886.
The following images were found in Dietrich’s email attachment collection and are from an unknown source. They show a Drilling sold by W. H. Holstein and made by the Römer Werks in Suhl.