What it is
NAS1291 nut, thread .4375-20UNJF-3B (ESNA LF3858-7, catalog p.23 / PDF p.25)
Equivalents
No equivalent on file: no maker document names one and the government catalog lists none on its stock number.
Install tooling, by who made the part
Not documented for this part number. Ask a tooling specialist →

Reference only: the drawing and its process spec govern. How to read this

Every size and maker in the NAS1291C series →

Full detail: decode, cited documents, every stock number