I need to replace it in one of my A1181 MacBooks but there are 2 fan sizes. How can I be sure I'm getting the right size? I need the smaller fan version.
This should help you identify which you need. https://www.ifixit.com/Guide/MacBook+Core+2+Duo+Fan+Replacement/522
Note there are a fan for older Macbooks, and also one for the SantaRose/Penryn models, which would be the newer ones. Looks like the smaller fan is for the older MacBooks, but you would need to check that out yourself.