In space, if unprotected pieces of metal touch each other, they stick together permanently.
This doesn't happen on Earth, because the oxygen in our atmosphere forms an extremely thin film of oxidized metal on every exposed surface. The oxidization layer acts as a barrier that conveniently prevents chunks of metal from sticking to other chunks of metal.
In the vacuum of space, however, there is no oxidation layer. If the atoms of two metal objects come in contact with each other, what you suddenly have is one continuous metal object, and a lot of explaining to do to your mission commander.
This is an issue on the space station. Metal tools used outside the station have to be coated with plastic or other materials that will not stick.
got it from here:
http://www.coolsciencefacts.com/2006/metal.html