This is a Macbook Pro 15" Left fan assembly. (When looking at the machine as you normally would.)
To determine which fan you need, look on the bottom of your machine. In the block of text that starts... "Designed by Apple in California...Model Number", the model number of your machine is the type of fan you need to order. So, for example, if the model # on the bottom of your machine is A1150, then you need to pick the option below with A1150 in the description.