UPDATED - 7/1/16.... Just another TTT for an old how-to thread wherein I was schooled on galvanic corrosion.
Original post follows.....
I needed more room than the stud allows on the battery terminal of my starter relay/solenoid, so I decided to add a coupler and a bolt - that way I could put a few of the wires on the stud side and the remainder under the bolt. But, the only couplers I could find commercially were made of steel - not very good for conductivity. So, I made my own using some 1/2" copper hex stock from McMaster-Carr and an aluminum bolt. A few minutes on the lathe and the hex bar was drilled out and tapped. I'll finish it off with a little heat-shrink over it once it's installed for good just to give the electrified surface a little protection. Overall, it will make for a cleaner installation of the various wires I have going to and from that terminal.
Although I could have accomplished the same thing with a bus bar located nearby or under the dash, I thought this was a simple and functional solution.