As stated above, Ford dealer stocks them @ about $2.50 ea. There are a couple tricks you need to know about, however. 1. The plug is threaded on the inside and outside. 2. The outside thread has a locking compound on it which is a 1-time use product. 3. The inner thread is for bolting accessories to the engine - alternator, A/C, etc. It is a standard SAE thread. 4. The plugs have notches in them which allow you to screw them into the head using a large screwdriver. The problem you have, however, is that if you are using a screwdriver wider than the plug, it will hit the head, before the plug is all the way in and seated. Then when you discover this and try to back the plug back out, you mess up the 1-time locking compound. I never did find a screwdriver that was the exact right size to fit the plug. Wound up grinding one down. I put the plugs in a little deeper than the head surface. I then used a common short bolt with A/N washer & locktite to fill the hole on the inside of the plug. By tightening the bolt and A/N washer, I was able to put tension on the plug to make up for the weakened thread locking compound.