@stevro25 Thanks for contacting us today. It appears that you did order the 32GB kit for your system. If you purchased the iMac with the standard 8GB adding the 32GB to it would actually allow you to upgrade to 40GB of RAM as you can mix the RAM. CT10559878 is a 16GB kit. Adding this kit to 8GB of standard RAM would give you 24GB of RAM. Both kits are completely compatible it will just depend on how much RAM your system came with originally and if you mind having more than 32GB of RAM or not Please let me know if you have any other questions or concerns or if there is anything else I may be able to help you clarify.