Tip-ups are used ice fishing to allow setting up multiple lines and baits. You must check your local and state fishing regulations to determine if tip-ups are legal and the maximum number that a single angler can set. Some states allow three tip-ups per angler, but local lake regulations can either disallow their use or limit the number allowed. Ice fishing tip ups hold fishing line on a spool that is held underwater. The spool containing the fishing line being held underwater helps prevent freezing of the fishing line to the spool. The basic design has the spool attached to a metal shaft. The shaft extends above the water and has two nubs attached to the shaft. Usually one nub will be smooth and the other one on the opposite side of the shaft will have a groove or notch. A flagIce Fishing tip-up flag is attached to the base of the tip up with a spring mechanism. When your bait is lowered into the water below the ice fishing hole, the tip up is placed straddling the hole. The flag is bent over and held by one of the two nubs. The tip up should be positioned so that the nub you are using if pointed at the direction that the wind is blowing from. The two different nubs allow for either a smooth release of the flag if the spool starts rotating or the notched nub allows a little more tension. When a fish grabs your bait and starts to swim away, line will pull from the spool. The spools rotation turns the shaft, which will then rotate the shaft away from the flag that is secured in place by the nub. The result is that the flag will pop up, which signals a fish has bit the bait.