I cleaned the ground cable connections on my 500 amp Shunt.
Those bolts have 9/16" heads. The 2 smaller flat head screws are for the sense wires which goto my battery monitor, which counts ALL amperage into and out of my batteries.
I also added another 4 awg cable from the Shunt to the House batteries. This in theory should allow more alternator current to make it into the house batteries when they are low, and the engine is turning the alternator fast enough.