Raimey, you should throw away your magnifying glass and undo your blinkers. Both seem to narrow down your field of view in a most dangerous way. Of course, none of the post-1900 Suhl barrel- or gunmaking Kletts had a steelwork of their own. Gunmaking Kletts are mentioned in Suhl since 1490. Many of the early Kletts were barrelmakers. During the 1500s -1700s they sold musket barrels all over Europe, to arsenals as far away as Zürich, Bern and Geneva. In the early 1600s, the time of the 30 years war, a branch of the family emigrated to the Salzburg area, working for the archbishop there. Many of these early Kletts used the “Klettblume” = burr flower as their mark, one to three burrs, often on stalks. Read the chapter on the gunmaking Kletts in Fritze’s book “Suhl – Heimat der Büchsenmacher”.
But there are many more families named “Klett” in Germany, not related to the Suhl Kletts. German Wikipedia lists no less than 18 persons named Klett, none a gunmaker, and the Klett publishing company. The most interesting when it comes to “Klett steel” is Johann Friedrich Klett, 1778 – 1848. He may even be related to the Suhl Kletts, as he was born in Zella. In 1841 he founded the ironworks Klett & Co in Nuremberg, which later became part of the MAN combine. So maybe MAN later tried their hand in supplying barrel steel, using their old Klett steel label. Or, one of the barrelmaking Kletts, the “K in burr” mark is visible in the photo, bought in a noname barrelsteel and marked it as “his own”, not an uncommon procedure in the German guntrade.