To avoid those awkward moments when you wish you had inserted a T-nut in your newly mounted delta (or any other open-build based machinery for that matter) to secure any accessory...
This one can be introduced into the slot from the top, no need to access from the side.
Thank you who?
The part is symmetric, just be sure not to print them too close to each other (they could stick together). It requires a fine-tuned printer, so your mileage may vary (you may have to play with some offset in your favorite slicer).
Not to support heavy accessory.
Made for an M3 screw.
Drawn with Onshape. Public Model.