Choose your memory based on your model MacPro.
Locate MacPro model identifier
MacPro6, 1 (2013). December 2013 - present
MacPro5, 1 (2010 & 2012 releases)
MacPro4, 1 (2009). March 2009 - August 2010
MacPro3, 1 (January 2008). January 2008 - March 2009
MacPro2, 1 (8 Core). April 2007 - January 2008
MacPro1, 1 August 2006 - January 2008