That's a water bond fitting. They are required in many areas now and needed if you don't have standard light niches that act as the water bond.
Your #8 solid copper bond wire will run through that lug and on to the pool equipment.
I bet your inspector called them out on not having one
Your #8 solid copper bond wire will run through that lug and on to the pool equipment.
I bet your inspector called them out on not having one