I lost an m7 set screw. What do I do?

M7 set screws are impossible to find in hardware stores. So instead of paying out the wazoo for a single screw online, is like to find another way to safely hook up the power cable on my amp. (I found an m7 bolt in lowesb afraid it'll arc and cause a fire if I use that)

Is there a way to solder this 4 gauge wire to the amp?

Its for a class D monoblock subwoofer amplifier in my car.