RE: Everything Radial Engines
You can also use a piece of silicone fuel tube (with the smallest inner diameter) to help start the plug onto the cylinder head. Do this by pushing the electrode of the plug onto the tubing. Then, begin to thread the plug onto the cylinder using the tubing as an extension. Once you have a few revolutions on the plug just pull the tubing off the plug and finish tightening with the wrench. This is a great way ensure the threads of the plug are meshing correctly with the threads from the cylinder and will ensure against any cross threading.