SPARKY.

 I wanted an easy job first thing this morning so decided to have a look at a spark plug. I find it difficult to work things out but this was easier than most.

The centre positive electrode is tungsten, free in small diameters as it is used for TIG welding electrodes and welders never use the last inch or so. The white insulator can be machined from Teflon or PTFE(Same stuff) and high temperature glues are readily available to stick it all together.

The only things missing are the 6mm thread on the bottom of the body and a 1mm thread on the top for connecting the HT lead. The reason they're not there is the computer would most likely say no and I wasn't in the mood for lots of special words. The complete plug is about an inch or 25mm tall so not very big at all. 

I even popped Adrian's Images on to the surface of the insulator in a subtle manner. I must be going down with something as understatement is way out of character.

The next job is to learn how to use the Assembly Workbench in FreeCAD, not something I'm looking forward to. There are plenty of 'Howtos' on YouTube but a pound to a penny the ones I want are in Russian or Hindi.

Have fun.