cylinder head question - Never saw this before

[jeep_n_john]

So I was removing cylinder head from spare engine and Did not notice this until I got it off. 3 of the 4 spark plug holes have some kind of adapter in them. I do not see how this works as the electrode would not even stick through the head. I can only suspect these were an attempt to fix a stripped hole, but hard to believe 3 of 4 were stripped. If they did 3, why not just do the 4th one for consistency.

Has anyone seen this and explain? does this even work? Pics attached.

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