There is only one file type that uses the .JT extension:
JT Open CAD File
Lightweight 3D model format developed by Siemens PLM Software; designed as an open, high-performance, compact, persistent storage format for product data; used for product visualization, collaboration, and CAD data sharing.
JT files may contain approximate (faceted) data, exact boundary representation surfaces (NURBS), Product and Manufacturing Information (PMI), and metadata. They may be exported by native CAD systems and imported by product data management (PDM) system.
NOTE: The JT format is primarily used in the automobile and aerospace industries but is suitable for all manufacturing industry applications.
Updated: February 15, 2014