RAM & Memory Upgrades
Timetec Hynix IC 16GB(8GBx2) DDR4 2400MHz PC4-19200 SODIMM Memory Upgrade For iMac Retina 4k/5K 21.5-inch/27-inch Mid 2017 (Single Rank))
DDR4 2400MHz PC4-19200 260 Pin Unbuffered Non-ECC 1.2V CL17 Single Rank 1Rx8 based 512x8 Power Supply: VDD=1.2V (1.14V to 1.26V) VDDQ = 1.2V (1.14V to 1.26V) Module Size: 16GB Package: 2x8GB Compatible with Apple iMac 2017 iMac18,3 w/Retina 5K...
https://www.bizrate.co.uk/ram_memoryupgrades/timetec-hynix-ic-16gb-8gbx2-ddr4-oid9146760346.html