ER6n part# is 16163-0138
Ninja 650 # is 16163-0141
Both are listed as a TTK38. Different part numbers, there will be something different. But it's been my experience that if the first 5 numbers are the same, as it is in this case, they should interchange.
I would say give it a shot if you can't find the one for your bike. Then worst case scenario, you should be able to resell if it doesn't work.
Purchased new in July 2006, 0 miles.
Miles as of January 2019 102,137 miles