I lost the bulkhead for my flex and couldn't find one. Save yourself 10$ and just print this one. I used this nozzle with it. Enjoy. 

https://www.printables.com/model/819851-fluval-flex-15g-low-flow-spray-bar
 

Supports aren't necessary, print hexagon side on the build plate

The thread is m20x2 in case you want to modify or recreate it