The NAS1763D121008 is a factory-new T-fitting (tee) supplied with traceable paperwork for certified maintenance. A tee is a three-way pipe/tube fitting that joins or splits fluid or pneumatic lines, keeping flow paths sealed and aligned. This part restores the original routing and connection geometry where the aircraft IPC/AMM or OEM drawing specifies this number. https://gfa.aero/aviation-parts/expendables/NAS1763D121008