These rings have no official connection with the SS or Heer Panzer forces. They were simply private purchase rings any soldier, sailor or airman could buy. They could be purchased via mail order from newspaper adverts or purchased in soldiers canteens.
Having said that, they were very popular with the SS and Heer Panzer forces due to the Deathshead connection.
Great item by the way!
Cheers, Ade.