Most transport size freighters have some version of that in the floor to use as a receiver for strap tie-downs. What is on the bag is literally the same thing, made of the same material. The bag hooks you can buy use a simple plunger mechanism (same as a plane would use at the end of the cargo strap) to attach to the rail and you hang your bag there. Much better than a hook like the most common bag uses that has a fabric strap and swings around, stretches, etc etc etc. Photos of the hook and how it attaches at https://paradoxaviationllc.com/produ...ck-accessories