I can't say with absolute certainty but I think it is a part that was upgraded with the fully prepunched RV-8 fuselage.
I think the part is now supplied with two halves and the required spacer, joined to each other. Break apart the three parts, deburr, and rivet.
That's why it only calls for one part (#) needed. (I Think)
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Van's Aircraft Engineering Prototype Shop Manager
RV-6A (aka "Junkyard Special ")