Question:  It says a 347 (or 348 or 349) will protect an eight wire rotator cable.  But the picture shows two rows of screw terminals with only 8 screws visible.  How does this wire up?  it appears there aren't enough screws.  

Answer: The rotator/control line arrestors don't wire with an "in" and an "out" screw.  Of the eight wires in your cable, the yellow wire from the rotator and the yellow wire from the shack both go to the same screw. You can cut the wire and put both ends into the same screw or put both ends into a spade terminal and then put that into the screw.  If we put twice as many terminal strips on the unit to accomodate an "in" and "out" screw, it would cost a lot more.  See pic. Also RTFM :-)  :-)

                                                              This M-348 only has a four wire cable on it at the moment, with four terminals unused.

Question:  Which model should I use for my Yeasu rotator?

Answer:  Every Yaesu and Hygain rotator uses an M-348.

Question: What if I have an eight wire cable and want to protect four additional 12v wires, can I put all twelve of them on the same M-348b unit?

Answer: Yes you can run more than one thing on the same M-348 unit.