I bought a set then realized you can make your own. It has been a while but I believe you use 1/2" copper plumbing end caps. I eye-balled what I thought was the inside center of the end cap. Marked it with a sharp punch then drilled a hole for the spark plug contact to stick through. If the hole was off center I rat tail filed it until if fit better. I use them on my W18 Champion plugs.
Bob-A
