Thanks Rick, I wish I found this post before. I had the same problem and spent more time searching the internet for the bolt and bolt size then I did taking them out and putting them in. I needed 8 - PAIR manifold plugs for my 86 K30 350 engine. I found them at NAPA - Part #: NOE 7041048 (they are oil drain plugs). They only went in about half way, and cost about $40, but turned right in no problem.