The washer is the bottom of the bushing for the strut mount. In stock form (on my tracker) the washer for the bottom of the strut mount was installed inside the shield, keeping the shield at the top. When I installed my extensions I noticed that the shield would come up so high that the lower part of the strut rod would be exposed. I wanted to keep the strut protected like it is stock so I installed a washer on top of the strut to hold shield up, then installed the exenstion, and inserted washer, bushing, washer and nut into the strut mount. I also used some rtv sealant to keep the keep the shield in place so it doesn't move up and down or rattle.