(Ok I admit, I couldn't resist the title).
Several people have asked what the extra metal screw/nut is for in the kit. In the final version of the magazine article we left off the instructions for using the metal screws to align the battery clips for soldering (see Step 15). Here's the full description of what to do.
Installing the battery clips
The screws supplied in the kit are nylon with nylon lock washer nuts. Although not absolutely necessary it is preferable to run a bead of solder on the inside of each battery clip. To do this you will need a metal 6/32 screw and nut. Start by using the metal screw and nut and attach a battery clip to the front and back side of the pcb. Check to make sure it is aligned and run a bead of solder down the inside of each of the battery clips (front and back) Once the clip has cooled remove the metal screw and repeat the process for the clips on the other side of the tree. After this side has cooled remove the screw and replace with the nylon screws and nuts. The nuts supplied in the kit are lock nuts and will thread on the screw with some resistance. Also since they are plastic screws please be sure to avoid over tightening.