These work great with chunky crochet patterns like the one in the image which was made with a 5mm hook. They are easy to attach to the pattern with a darning needle and some extra thread. Some letters have variants with 2 loops to aid with secure attachment.
Print face down without supports. Consider using a textured build plate for an interesting surface pattern to the letters.
I included the SCAD file so you can easily make your own set with a different font or create new shapes to attach the sewing loops onto.
The author hasn't provided the model origin yet.