Ordered to replace a 27 year old Nutone fan motor. The piece of sheet metal on which the new motor will be mounted is the right size to fit in the existing box. Set the screw hole lines. The item is declared as a replacement for several different models, including mine. I had to cut enough metal with scissors to fit two sockets in the fan box. No big deal but be careful. About 20 minutes work. Having made the rectangular hole for the outlet about half a centimeter longer, the replacement hasn't worked yet. The new device vibrates and therefore makes significant noise. The original was also a bit noisy, only the new one is about 60% louder. This is not very bearable for me or for the family. Communication with the seller to find a solution. My advice, if you're ordering this to replace your old unit, save your old fan for spares. An old squirrel cage fan may be quieter than a new one, so it can be installed on a new motor. Unfortunately, mine ended up in the trash can and disappeared.