We can give you the correct machine by using your serial number, then give you the correct part number.
Using the EMC number, your machine is one of these two: http://www.everymac.com/ultimate-mac-lookup/?search_keywords=2555
MacBook Pro "Core i5" 2.4 13" Late 2011 2.4 GHz Core i5 (I5-2435M)
Intro Date: October 24, 2011 Disc Date: June 11, 2012
Order No: MD313LL/A Model No: A1278 (EMC 2555*)
Subfamily: Late 2011 13" Model ID: MacBookPro8,1
Std RAM: 4 GB Std VRAM: 384 MB
Std Storage: 500 GB (5400 RPM) Std Optical: 8X DL "SuperDrive"
Complete MacBook Pro "Core i5" 2.4 13" Late 2011 Specs
MacBook Pro "Core i7" 2.8 13" Late 2011 2.8 GHz Core i7 (I7-2640M)
Intro Date: October 24, 2011 Disc Date: June 11, 2012
Order No: MD314LL/A Model No: A1278 (EMC 2555*)
Subfamily: Late 2011 13" Model ID: MacBookPro8,1
Std RAM: 4 GB Std VRAM: 384 MB
Std Storage: 750 GB (5400 RPM) Std Optica