Convert your STL (stereolithography) shape in to a solid body, save it as a STEP file and then import it in your 3d modeling software and save it as ACIS (one body, if it isn't already.. ), than save it as a PART file.
The easiest (and fastest) way is using FreeCAD, which is free software, and you can download it on the following link:
https://www.freecadweb.org
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#3Dmodeling #spine #SolidWorks