This product is either discontinued or we cannot get that from suppliers.
Kingston Dimm Hx426c15fbk4/16, 16GB (4 x 4GB), 288-Pin DDR4 SDRAM, Speed DDR4 2666 (PC4 21300), CAS Latency 15, 1.20V, Non-ECC, Unbuffered, Compatible with Intel X99 chipset.
HyperX HX426C15FBK4/16 is a kit of four 512M x 64-bit (4GB) DDR4-2666 CL15 SDRAM (Synchronous DRAM) 1Rx8, memory module, based on eight 512M x 8-bit FBGA components per module.