The cheap wood ones you can order are not uniform and are sometimes unusable because the screw holes are too close to the hoop to be tightened properly. They can also discolor your creations. This design needs no screws, encloses the back cut fabric ends and has optional tools to make mounting a breeze.

Tolerances are tight. I used PLA+, 0.4 nozzle and 0.2 layer height.  No supports should be necessary.
 

Instructions (Photos after the model files roughly correspond to steps):
 

1. Cut fabric for display in a 2.5" circle with the embroidery or cross stitch centered.
2. Place the front disc on the mounting cylinder with the threaded post in the middle of the cylinder.
3. Place fabric with pattern facing up on the front disc centered.
4. Line up the top of the fabric with the notch of the install tube and push the tube down over the fabric. It should be a good fit that keeps the fabric tight.
5. Remove the mounting cylinder and make any needed adjustments to align the top of the fabric with the notch of the install tube. Don't let the fabric come loose.
6. Place the install tube over the embroidery hoop. The notch will align with the top of the hoop.
7. Use the plunger to push the fabric and top disc down tightly into the embroidery hoop.
8. Slide it all off the work table edge and hold it together with your fingers as you flip everything over.
9. Align the back disc so that the threads on it and the front disc align and tighten it down with your fingers as best you can.
10. Insert the 5mm hex with knob tool into the back disc and using a decent amount of downward pressure finish tightening it down.