RAM & Memory Upgrades
64GB (4 x 16GB) DDR3 1866MHz PC3-14900 240-PIN ECC REGISTERED DIMM (RDIMM) MEMORY RAM KIT COMPATIBLE WITH MAC PRO (LATE 2013)
SIZE/CAPACITY: 64GB KIT (4 x 16GB) VOLTAGE/POWER CONSUMPTION: 1.5v CAS LATENCY: CL13 SPEED: PC3-14900 (1866MHz) TYPE/INTERFACE: 240-PIN DDR3 ECC REGISTERED DIMM (RDIMM) 240-PIN MAC PRO DDR3 ECC REGISTERED DIMM RDIMM KIT
https://www.bizrate.co.uk/ram_memoryupgrades/64gb-4-x-16gb-ddr3-oid6611133854.html