Caogang or Useful Steel Channel.
Steel shaped for use in construction. channel steel is used for cross-sections. With 5 cm channel steel you can construct the base of a mezzanine, and on this mezzanine you can stow away all the things you never like to see but are unable to throw away, until one day you seal it off entirely and tell your friends that you did it in order to improve the house insulation.**
*He crossed the street then left his medical bag on a green trash bin and started running away as fast as possible. The footsteps behind him made a continuous mark called Line, but maybe a Lion.
**He kept on coming back from afar to a closer distance; his ears are malachite green and eyes are emerald. But his tears are colored rats bane, his face the size of a one RMB coin, so small that from a distant place that should be called face, it looks more like the bold back of a head with a strange spot in the middle of it. His name starts with F.