crazydave
Member
Hi there, Its not any sort of compression tester, Why would it have an earth electrode? Its a shielded spark plug, used to suppress radio interference, and also offers some degree of water/ splash proofing. They're quite often used in aircraft. God only knows why it fell out of yer lanny, Have you found any wings lying in the road behind you? Here's a pic of a new one: Champion Spark Plug Type from Aircraft Spruce