How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
Adamanta 16GB (1x16GB) Memory Upgrade for 2017 Apple iMac 27" Retina 5K Display DDR4 2400Mhz PC4-19200 SODIMM 2Rx8 CL17 1.2v Dual Rank RAM DRAM - Walmart.com
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
Apple iMac 27-Inch with 5K Display Review (2017): Serious Power | Tom's Guide
iMac with Retina 5K Display 2014/2015 Memory Upgrades
Apple 21.5-inch 4K iMac Teardown Reveals Upgradeable Kaby Lake CPU And RAM | HotHardware
Apple iMac (27-inch, 2017) review: Apple doesn't mess with success - CNET
A-Tech 64GB (4x16GB) RAM for Apple iMac 2017 27 inch Retina 5K | DDR4 2400MHz SODIMM PC4-19200 2Rx8 1.2V 260-Pin SO-DIMM Memory Upgrade Kit at Amazon.com
iMac Retina 5K: Memory upgrade (RAM)
Install memory in an iMac - Apple Support
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 2017 5k iMac RAM to 64GB & Saved $840 | 2018 - YouTube