Buying a New iMac? Here's What You Need to Know About 2017 iMac RAM Upgrades
16GB Apple iMac 2017 21.5" Non-Retina RAM Upgrade iMac18,1
Upgrade your iMac 27'' 2017 RAM with MrMemory review - Wim Arys
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
512GB 4X128GB NEMIX RAM Memory for Apple iMac Pro 27-inch Late 2017