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Amazon.com: Rinbers 2.5" 9.5mm SATA HDD SSD Caddy Adapter Bay for Apple MacBook Pro 13/15/17 Inch with CD-ROM Drive A1278 A1286 A1297 : Electronics
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Installing MacBook Unibody Model A1278 Dual Hard Drive - iFixit Repair Guide
Hard Disk Drive Adapter SSD HDD Caddy for Apple-MacBook Pro A1278 A1286 A1297 - AliExpress
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Amazon.com: HDD SSD SATA Hard Drive Connector for Pro 13" A1278 Pro8,1 Early 2011: MC700LL/A MC724LL/A Late 2011: MD313LL/A MD314LL/A : Electronics
How to install SSD in MacBook Pro A1278 | Hard Drive replacement - YouTube