This is a variation of the Trefoil Knot that I made for my undergraduate research project.
The .stl file was made using Mathematica's RegionPlot3D with a PlotPoints of 200.
Read more about about the trefoil knot on Wikipedia.
Read more about my projects on my website.
The .stl file is large due to the high resolution model Mathematica generated. The model is fully scalable to 3D print at any size.
Note: Depending on how small you print the knot, the center can become very skinny. I recommend setting the infill % to a higher value to prevent breaks and snaps (or add more shells).