My goal is to have the SNAP-UDC-HDB near the SNAP-ODC-32-SRC module, within 6" -12" inside the same electrical enclosure. Opto 22 sells the cables at 6ft lengths, this works great when you have the PAC Rack separated from the SNAP-UDC-HDB at that distance. I researched for an alternate method of connecting them. Turns out that a 40 pin hard drive cable works! I purchased 12" length cables for $6 each. Note the cable must have pin 20 open, not filled in for it to work. Attached is how I connected them, note the red indicator on the cable for the correct orientation for connections.