This is the roundwound string that James How and John Entwistle perfected into what was to become the industry standard.

The bright, punchy, high-energy sound of Swing Bass 66 strings is a major part of early rock music history and brought the bass player from the back line to the front of the stage.

https://www.oosthavens.co.za/product-category/strings-things/strings/bass-guitar-strings/