[Jon Stratis]

PAR - The nut and bolt aren't involved all that much in the electrical pathway. The electricity will primarily flow from the battery terminal through the lug terminal on the end of the battery connector. This is due largely to the large surface area connection between the two, which makes it a much, much more efficient conductor than going "out of your way" to travel from the battery terminal, through the head of the bolt, down the bolt, into the nut, and finally into the terminal on the end of the battery connector.

True, any time you have conductive materials attached together, all of the materials involved will conduct some electricity. But in this case, it's not enough to make it noticeable. Essentially, you have a current divider circuit, with the two sides of the circuit having significantly different resistances. Play around with that, and see how changing each side of the circuit can change the overall current through the circuit.