A rubber (viton-fuel resistant) sealing ring that seals between the air filter cannister and the alloy adaptor on the SU carb 1-1/2" (HS4).
It suits mini, and Moke/Morris 1100 and Mini Automatic with the larger filter and needing an oval ring.
It is essential for long engine life. We also sell a round ring for the smaller filter or twin carbs.