OK, every truck has at least a few of these types of clamps.
It is called a Marman clamp.
The thing was invented by Herbert Marx and produced by his company Marman Products Company, Inc.
It was used during the war for a lot of different things but the really important purpose was to hold the Atomic Bomb in place in the Enola Gay. It is still used for all kinds of things, including the space shuttle and an awful lot of trucks.
Now who is Herbert Marx and why is he really important to us?