Assemble one rivet as shown, put some grease between the washers. Insert it
into the subframe and start tightening the bolt while holding the white
threadless nut with a spanner. The nut will bite into the rivet and prevent
it from spinning, so the bolt will start deforming the soft rivet as it's
tightened further. Eventually the rivet will become tightly seated in its
hole. Remove the bolt and proceed with the second rivet.