Just got a reply from Gold Plug .. (FAST)
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Brent,
Thanks for the email and sorry for your troubles.
This is a problem we found out about last week. One of our contract machine shops incorrectly added those serrations to a small batch of MP-11 plugs.
I will have the correct MP-11 shipped today at our expense. I am sorry for the error.
Thanks,
Tim
Gold Plug LLC