To upload an STL 3D model without converters, use tools or platforms that natively support STL (so you can upload files directly without converting).
Common options include 3D printing services (e.g., Shapeways), design software (e.g., Blender), or sharing platforms (e.g., Thingiverse).
Since STL is a standard 3D format, just check a tool’s "supported file types" section first—conversion is almost never needed.