That washer goes under the head of the grade 8 bolt. The bolt head welds to the big square washer, and the big square washer welds to the riser bracket. It basically increases the thickness of the riser in that location. I’m not sure that you can attach the riser bracket at the full width pin location. I’m not sure that you want to, unless you are building a custom track bar. Better make sure that the radius arm has room.