Hi and welcome to the forum! Music Man truss rods are single action. It makes little difference in actual use, you make the same adjustments the same way when ever they are needed.
I don't know the manufacturing specs of the rods they use. A quick google search produces a result from 2010 that says on guitars it's 10-32 and 1/4"-32 on the basses but I'll not guarantee it. Feel free to call Music Man directly and ask.