These parts are accents for Transformers WFC:Siege Autobot Six-Gun. These small fins for the upper legs are meant to homage the details from the original G1 toy and animation model.
The parts simply plug into the slots on Six-Gun's leg. They are directional, so make sure you have them oriented correctly when installing.
The two fins will be printed with a very small sprue connecting them. This is to reduce the price.
Photos are from my own Prusa i3 MK3 3D prints, not Shapeways prints.
Printable STL files for this item are available for purchase on Cults -
click here.