This is a T-handle hexagonal wrench used for tightening or loosening hexagonal nuts.https://www.printables.com/model/70527-ufs-094-t-handles-hex-allen-key-wrench,https://www.thingiverse.com/thing:4716243)。

While working on a project, I repeatedly inserted and removed the Allen wrench from the T-shaped handle, which inspired me to come up with this design.

You can also find this product on Printables:https://www.printables.com/model/418887-t-handle-wrench