These are useful when installing a pair of emissions legal heads on a non-emissions car. All OEM and aftermarket Ford smog legal heads have thermactor holes, one on each side of the head.

Each cylinder head takes 2 plugs. Check out our other items if you only need 2 plugs.

All OEM and aftermarket Small Block Ford heads have thermactor holes. These plugs block the holes for use on non-emission cars, and are internally threaded for accessory mounting. For use with GT40,GT40P, Trick Flow, World, AFR, etc.

Compare to Summit Racing/Trick Flow at almost $10.00 PER PLUG!

Some of these are silver in appearance, some are black hardcoat, all work equally well.

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I added a picture of a plug installed in a head. This is the intended use of these plugs. These plugs do not work as 02 sensor plugs.