These coupler bolts are what holds your River Quiver fly rod holder together.
This product comes as an replacement set for either 2-Banger or 4-Banger River Quivers.
They aren’t huge, so you may have misplaced them, or your industrious kid may have taken them out and lost them. It’s necessary to have all coupler bolts installed properly, so if any have become lost or damaged here is where you can find replacements.