Difference between these 3 intake valves?

I've scoured the internet for the answer to what I thought was a simple question, but I cannot find it anywhere so I gave up and turned to the forums. There are 3 intake valves on a 2007 yz250f. According to the yamaha parts manual, the center intake valve has a different part # from the other 2 outer valves. I have also noticed on websites selling aftermarket valves they will list a specific "center" intake valve for my bike , and regular for the outer two. I need to know the difference between these valves because my three intake valves got mixed up in shipping in the package..
 
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