My water diverter is screwed on to the outdoor faucet, but now it's stuck and it won't budge in either direction (black connector in images). It has four equidistant "notches" intended for gripping, but they actually make it more difficult to grip with a tool.
What I've tried so far:
- turning by hand (with towel to avoid finger bruising)
- "chisel" technique with screwdriver and hammer against one of the notches
- tried to grip with wrench, but can't fit a round more than one notch
What tool or technique is best to get this unstuck?