Hey, it is a nut! I wanted to use this 1/4" waterline adapter for the filament feed-through on a drybox I am making for printing with Nylon. I hadn't been able to find a standard nut for these 1/4" waterline adapters so I made one. I measured the threads using the 3 wire method. For those that care, I measured 18 Threads per inch and a pitch diameter of 0.481". I made my pitch diameter 0.492". Major diameter is 0.529". It fits perfectly. IGS file included if you want to tweak it.