like Kev said... put 2 5" clamps together and you will be all set... As long as you buy them at the same time they will fit together just fine.

I'd put at least 3 sets on the tank... that way if one fails you have 2 more to hold it on. I'm guessing that thing will see a lot of vibration back there. Occasionally the screw mechanism on those clamps will fail.

 

Try a tire store if your hardware stores don't stock them. Most have clamps they use for wheel sensors.