This is an original early Blau 110mm fuel cap, it is an ALL Aluminum cap, the top and center-bottom unlike the many common others made from steel. It was removed from a 917K and was given to me by Gustav Nietzsche https://pbase.com/917carl/image/22303465 who brought it all the way from Germany on one of his many U.S. visits (Gustav Nietzsche was here to help build Carl Thompson' 917K from the ground-up! You can see photos of the build here https://pbase.com/917carl - Don't miss that photo gallery!).

Thanks again Gustav!