This is a frame rivet to attach parts to the frame. The rivet has a 3/8" shaft and is 7/8" long with a round head and will attach two parts to the frame like the shackle bracket and the bumper gusset. These are only used in a few spots but is a must have part! These are great to get that authentic restoration!
If you don't have the tool to attach this rivet we have that too!