I wanted a more robust drop-in T-nut for my Prusa 30x30 rail. Warning Straight off the printer they will go in but it will be difficult to get them back out. A quick sanding to the outer edges will allow them to come out easier. The hole is solid for .2mm (1 layer) so you can print flat with the square side up. Punch a bolt through the single layer in post processing.
.2 layer height
4-6 perimeters 20%+ infill
The author hasn't provided the model origin yet.