Runners are the four ice skates upon which the bobsled rides. Minute variations in forging, alloy composition and shape make for huge performance differences and a mind-boggling number of possible combinations. Each athlete on a four-man bobsled is responsible for preparing one of the four runners for race day, a process which can take three hours of sanding alone. An athlete starts sanding out the largest scratches with 50 grit. He moves to 100 grit to sand out all of the 50 grit marks and keeps progressing until he is working with 3000 grit, and finally, diamond paste. This large hunk of metal stores the heat of all the continuous rubbing. The challenge, then, is to cool the runner enough to where it is within set bounds of the legal temperature.