The M939 cargo beds have stake pockets for the troop seats/cargo covers. There was a factory bolt-in tie-down option for these pockets, but these are extremely rare, and have a terribly sloppy fit, which beat up your bed sides. They also only worked on the middle pockets but not the ends.
 
My zinc-plated, laser-cut, TIG-welded, bolt-in tie-downs feature a locating shim to hold them centered under the bed side, as well as a cover washer to allow you to tighten them firmly. They come in 2 sizes: "Ends" and "Middle". An M923/925 bed has 4 "Ends" and 3 "Middle" pockets on each side.
 
Eyebolts are not included, but can be ordered from McMaster-Carr, HERE.
They are 3/4-16 x 2".