Got the plugs from my machine shop that conditioned my heads and took them out to install them, and i only got them about 2 threads in by hand then put a bolt in to turn them in and only got another thread or two and they stopped and i couldn't even take them out with the tabs to screw them in with the screwdriver and they just shredded. I had to take them back out with pliers. Is there something i did wrong here or are they just that dang tough?

 

Ok figured it out thanks for all the help guys

 

what was wrong?

 

The threads were all gunked up with carbon. Just took a tap to it