2017 21.5-inch 4K iMac memory upgrade kit includes 32GB of RAM, tools to take it apart | AppleInsider
How to upgrade RAM in the (Mid 2017) 5K iMac and save up to ~$900 [Video] - 9to5Mac
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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
Amazon.com: Mid 2017 Apple iMac with 3.0GHz Quad Core i5 (21.5 inch Retina 4K, 16GB RAM 256GB SSD) (Renewed) : Electronics
iMac 21.5-inch 4K (2017) Review | Trusted Reviews
Amazon.com: 2017 Apple iMac with Intel Core i5 (21.5-inch, 8GB RAM, 1TB Storage) - Silver (Renewed) : Electronics