Tap One Side

Using a 4-40 thread tap tool, cut threads into one of the brass strips. Don't force the cut: back off if it gives resistance and clean the cutter. Be careful to keep the tap at right angles to the strip from all sides. A crooked tapped hole can ruin a joint.

Cutting fluid will help here if you have it. I usually just use automotive oil, and it works great. Probably any oil will work.