This product is either discontinued or we cannot get that from suppliers.
Qnap NAS Accessories (RAM-16GDR4ECK0-RD-2666), 16GB DDR4 SDRAM Memory Module, RAM Module, DDR4 SDRAM, 2666 MHz, DDR4-2666/PC4-21300, Registered, NAS Server, 288-pin, FF DIMM.
Designed for their TS-2888X NAS, the 16GB DDR4 2666 MHz RDIMM ECC Memory Module from QNAP is a single RAM module that will let you upgrade the overall memory capacity of your compatible NAS.