when you screw in the ends it tightens the little things inside squeezing the wires. If that makes any sense. I have a fused 4ga. in 2-8 ga. out and a 4 ga. in 4-8 ga out unfused ill sell ya that i dont need anymore if you are interested. Just pm me if you are.
you put the wire through the part that comes out and fold over the copper over the end of it. Then you screw it in and it compresses the wire down securely.