This wear resistant nozzle by AVN/Micro Swiss is the standard size for a range of printers has a 5mm long M6 thread and 0.4mm tip hole. Total Length 13mm. The main hole is for filament with 2.85/3mm diameter or 3mm OD PTFE tube.
This is an aftermarket brass barrel for Ultimaker 3D Printers . It has the unique feature of a hex partway down the barrel to allow tightening without straining on other parts