GJS-500-7 also called GGG50 marks a strong and heat-resistant type of metal while GJS is a sign for Continuously Cast Spheroidal Graphite Iron - which describes a process in which the metal is continuously fed.
In 2025, the same photographer took the same cover but in a square frame from a different manufacturer - ULEFOS. The cover was taken at Strømsø Torg 1, Drammen, Norway Click for a larger image