Teardown of New 4K 21.5-inch iMac Reveals Removable RAM and Modular CPU - MacRumors
NEMIX RAM 64GB (4X16GB) SODIMM Memory Upgrade Kit DDR4 2400MHz PC4-19200 Compatible with Apple iMac
A-Tech 16GB (2x8GB) RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
How to Upgrade/Install Memory in a 21.5-inch iMac (Mid 2017) iMac18,1 iMac18,2 - YouTube
Timetec 32GB KIT(2x16GB) Compatible for Apple 2017 iMac (27-inch w/Retina 5K, 21.5-inch w/Retina 4K / Non-Retina 4K) DDR4 2400MHz PC4-19200 SODIMM MAC RAM Upgrade for iMac 18,1 / iMac 18,2 / iMac
Teardown of new 21.5-inch iMac surprisingly reveals user-upgradable RAM, modular CPU - 9to5Mac
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
Timetec 32GB KIT(2x16GB) Compatible for Apple 2017 iMac (27-inch w/Retina 5K, 21.5-inch
Adamanta 16GB (2x8GB) Memory Upgrade Compatible for 2017 Apple iMac 27"/21.5" Retina 5K/4K or Non-Retina Display DDR4 2400MHz PC4-19200 SODIMM 1Rx8 CL17 1.2v Single Rank RAM DRAM at Amazon.com
Install memory in an iMac - Apple Support
2017 21.5-inch 4K iMac memory upgrade kit includes 32GB of RAM, tools to take it apart | AppleInsider