From True Ames:
This fin was designed by the Campbell Brothers with the intention and specific purpose of being paired with their Bonzer Surfboards. This center fin is meant to complement the unique bottom contours and fin setups of their 3 and 5 fin designs.
The Bonzer fin works synergistically with the additional runners to efficiently and effectively organize water flow across the bottom of the surfboard, resulting in a highly optimal transfer of energy. If you have a Bonzer board, this fin is the official prescription prescribed by the Brothers Campbell to fix it up for maximum performance.
own it from $10 a week with More info