The inner sill is the vertical sheet metal under the door opening. When the car was built, this panel was part of the main floor pan. It is very important in that it forms a strong box section once the outer sill (rocker) panel is welded to it. This aftermarket panel is designed to replace a rotted inner sill, and includes a lower floor pan lip which allows the outer edge of the rusty floor to be cut away and replaced. It is notched to fit around the seat cross member, to facilitate an easier repair. However, if there is rust underneath the seat crossmember, we recommend removing the crossmember and using later inner sill SBO0110 (right)/SBO0111 (left) for a thorough repair before refitting the crossmember. For even more extensive rust, consider a half floor panel. Choose right- or left-hand side.