https://all4bikes.be/shop/images/schwalbe/schwalbe ventielgatadapter presta- 3640.jpg
In many cases the valve hole in the rim is much larger than your valve. Turn this onto your valves and your valve fits better in the rim, the chances of a leak at the valve will reduce to 0.
Suitable for Sclaverand / Presta / French valve.
For valve holes with diameter 8.25mm and more