Liquid metal-weld paste or gel This shouldn’t be used on structural components, among other things. The most popular brand of this type of miracle-bond is JB Weld. It really does have a thousand uses, but should never be used to try to repair damage on any structural things like suspension control arms or sub-frames. It also won’t help much to repair damage that involves a threaded hole that takes a bolt, such as cylinder head spark plug holes. Thread repair kits These are handy, but don’t bet your life on them. Nothing frustrates a home-tech more than wrestling out a seized bolt, only to have it finally come out with threads from the hole attached. Now if it was a spark plug hole, and you’re installing the engine’s last set of plugs until you scrap the car, a thread repair kit is certainly better than replacing a cylinder head.