Memory Upgrades for iMac 21.5-Inch 2012 - Late 2013
A1418 Memory SDRAM 16GB DDR4-2400 for Apple iMac 21.5-inch 27-inch A1419 (Retina 5K 2017)
HOW I UPGRADED MY iMAC 21.5in Late 2013 MODEL (SSD & RAM UPGRADE) - YouTube
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com