Westclox Factory Mainspring for Pickwick Travel or Pocket Ben Watch

Westclox Factory Mainspring for Westclox Pickwick Travel Clocks or "New Model" Pocket Ben Pocket Watches from the 1930's and 1940's (and perhaps beyond). Could also very well fit in other travel clocks and dollar watches. Original Factory Number was #6B where the newer P/N (shown on the envelope) is 650-7-8-30-49-5M. Documentation suggests the Dennison specifications of the mainsprings are roughly 26 x 2 x 20. New in envelope. Need a super thorough cleaning before use. This is the very last one I have. Images do a suitable job of representing the item.