From CoMakingSpace Wiki
Similar to scrap wood, we don't like to throw away metal parts and large leftovers that are still usable! We'll soon find suitable places for collecting these.
Things that are unlikely to be needed again are collected in a trash bucket - never go fishing in there without solid gloves!
Scrap metal is free to use, but please appreciate the work going into sorting and providing it - maybe you have a few minutes to return the favor at some point when the collection looks a bit messy? And of course you are still free to donate for a particularly nice piece ;-)