0.5mm upwards s large enough for most filtered debris to go through.
I have received your HFS-3 today. I have returned the controller (reflashed) via 1st class post. I have also put in a lower flow FAV and a new molex power harness.
I examined the power connector and cannot found any bad soldering joint. I tested the engaged molex conenctor by pushing and pulling it in all directions, not once has it made a buzz or flicker of any leds. Not sure what happen to you. I took a picture of the soldered joint and you can tell me where the bad workmanship is... The joints are untouched nor tampered with.
When you recieve the unit back, please let me know if the probelm, repeats itself again.