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The last few steps are to thread in the insert and drill one more hole for the roll pin that retains the insert in the head. The thread insert itself is hard-anodized aluminum rather than stainless steel. That’s why it’s the Ford-recommended repair. The aluminum insert has the same expansion and heat transfer properties as the cylinder head. The reasoning is that a stainless insert repair can cause overheating in that cylinder because it transfers less heat from the plug to the coolant than a repair with an aluminum insert does.