When it’s time to rebuild your two stroke top end, equipped with a TSP head insert, for your KTM/Husky 85, 125 or 150, you are going to want to replace the o-ring that goes inside the TSP head insert. These orings are a critical component to properly sealing the TSP head insert. We do not recommend reusing them. The kit includes one small o-ring and that seals between the TSP insert and the OEM head cap. These o-rings are made from the highest quality VITON material to withstand long term exposure to both chemicals and heat.