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I have a MacBook Air mid 2012 I cannot get the screws off the back of the computer with the tools.

Hello Debbie Long! To remove the bottom cover of your MacBook Air, you will need a P5 Pentalobe screwdriver. You can find one here if you do not have one: P5 Pentalobe Screwdriver Retina MacBook Pro and Air If you already bought an iFixit toolkit, you may already have this screwdriver bit and it just needs to be changed out for the current one on the screwdriver. Also, what kind of repair or upgrade are you trying to perform? I can provide extra guidance if you let me know.