Extremely rare Luftwaffe flight protection helmet (Fliegerstahlhelm) SSK 90. It was only manufactured for a short period of time in 1941. The only manufactured for this helmet was Siemens. The helmet was made out of interlocking and hinged steel plates that were designed to protect the head from shrapnel.  It was then covered with thick padding and dark brown leather. All straps are complete and soft.

The buttons are PRYM 6 marked. The liner looks to be made from the same material flight combination were made. Including the original manufacturing tag. 
Outside leather with clear signs of use and some damage. 

The size should be 62 according to the marking. Named to "Oberlt. Otto von Arght"