I would say 2 things. First, you will need the exact match of the model (for example A1237) plus the rest of the product specific (exact year of make). For example my model is A1237 but the upper case I bought didn't quite match especially the locations of the inner screws. I could not fit 6No screws back in when reassembling together. Without these screws the macbook air was put together and working ok but if you have a choice you want to get the exact match product. Secondly, screws. Some screws just won't come off. First thing you need a good screwdriver to unscrew a very tight and some are forced into position when assembled in factory. If you cannot take them out, take it to a computer guru who has the right hand. Seriously. I had problem with 3No screws they just won't come off. I forced it and damaged the screws. Luckily a specialist helped me to unscrew them and he told me that it's a known problem on macbook air. Other than that the replacement of the upper case was pleasantly done.
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