How tight is tight?????

[Olle]

Originally Posted by Dick Herman

Galling is much like surface contact welding. If there is a difference in the hardness of the steel screw (barrel) and the steel nut (receiver) galling should not occur. However using a thread lubricant greatly reduces the chance of galling AND improves the torquing efficiency.

I'd say it's very much like contact welding. Also, the increased friction and pressure cause microscopic tears in the surface, which will make them so rough that they don't want to slide anymore. I believe this is what happens in friction welding as well, right before the material starts heating up.

I have had the questionable pleasure of seeing that happen, and I thought I would never get the barrel off again. The shiny contact surfaces on the shoulders were dull and torn, just like if the parts had been welded and then pulled part again.