This is the best source of data that I have found on Pickelhaubes. The problem is that the books are impossible to find. If you gentle reader find one available, let me know I will buy it. It is in two volumes, hundreds of pages in German. It has similar line drawings to the Pietsch volumes. However, this one is very well annotated, well researched, and amazingly detailed in its documentation. Time after time, I find myself going back to these books. If you see them buy them. I cannot recommend them as a must-have because you can't find them. Many of the data bits that I have in articles are referenced to these volumes. Kraus goes back to the original source and pulls the data. It is a companion work to the one volume picture book of his that was printed in Austria. The single volume is available and highly recommended and has beautiful color photography and great text. This two-volume work has even better text, but alas no color photography.