iMac Retina 4K 21.5" 3.0GHz (Mid 2017) | mac of all trades
Teardown of new 21.5-inch iMac surprisingly reveals user-upgradable RAM, modular CPU - 9to5Mac
Apple 21.5" iMac with Retina 4K Display (Mid 2017) MNDY2LL/A B&H
Install memory in an iMac - Apple Support
Apple A Grade Desktop Computer iMac 21.5-inch (Retina 4K) 3.4GHZ Quad Core i5 (Mid 2017) MNE02LL/A 8 GB 1 TB HDD 4096 x 2304 Display Mac OS Includes Keyboard and Mouse - Walmart.com
A-Tech 32GB (2x16GB) RAM for Apple iMac 2017 (27 inch Retina 5K & 21.5 inch Retina 4K) | DDR4 2400MHz SODIMM PC4-19200 2Rx8 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
iMac 21.5-inch 4K (2017) Review | Trusted Reviews
Teardown of New 4K 21.5-inch iMac Reveals Removable RAM and Modular CPU - MacRumors
OWC Confirms New Low-End 27-inch iMac Can Be Fitted With 64GB RAM - MacRumors