This is a New Old Stock differential or compensating spring for a vintage Mercedes. From what I can tell, these were used on various chassis designations- 108, 110, 111, 113 and perhaps others. The stamped part number is nearly impossible to read but I believe it is 1103290501 and it has a post script of "1109". It also has painted markings that I believe relate to the strength of the spring. This came out of a closed restoration shop.