Lower Ball Joint bolts needed for K-H setup

I had some bolts picked up from the bolt specialty place today. I wrote down 9/16-20 fine thread, he sent back 9/16-18 fine thread, he said fine thread is 18 and not 20, I will admit to you, I do NOT know bolt threads and pitches worth a darn, so im asking, is it indeed supposed to be 9/16-18 fine thread or was it supposed to be 9/16-20 with another thread pitch? I am at work so haven't been home to try them, that's why im asking.
Thanks!