Yes there is an aluminum tube around the plug...
Ok....They are known as "drool tubes". That means you have a drool tube cylinder head. When you install new spark plugs you take the washers off.
The drool tubes act as the washer,when installed.
You will also notice some round rubber seals around the drool tubes. These seal the tubes to the cylinder head. When you get new plugs,get a set of new seals.
Felpro part# ES12794