OK, I'm not certain of the name of what I'm looking for, so maybe that's why I can't find it!
On a truck with a flat bed and stake and rail sides, you know, the horizontal boards, perhaps 2x6 or 2x8. At the ends where the side rails meet the rails across the back, there's a stamped metal plate to make that joint. It has a slotted "tongue" the mates with it's mirror image on the adjoining rail. Holds everything together, but slides out when you want to remove the sides. No tools required. There are some used to join parallel rails and some used for perpendicular rails. Maybe they are the same.
I need eight sets for the removable sides and back that my neighbor built for his utility flatbed trailer.
A place to purchase, or perhaps the correct search term would be appreciated.