They are rectangular, grey, and made of metal. In addition, they are very thin and have a circular hinge in the middle.
They are first encountered on level eight, and are only necessary to cross if the racer does not take the shortcut on level eight. When the racer lands on one, it will gravitate and tilt towards the side the racer is on. This can be either a hazard or a help, as sometimes it can jerk upward and send the racer flying into the air. They are helpful for crossing over pink lasers, though. However, sometimes it will send the player flying into a laser.