Which way does the rear sprocket go on?

[socialDK]

I received my new sprocket to replace my old, should have been replaced a long time ago sprocket.  Which side of the sprocket is supposed to face in and which faces out?  One one side of the new one it is completely flat, the other side has a groove all the way around about a 1/4 inch below the teeth.   The old one had a groove but it was much closer to the sprocket nuts and sat flat side in.

The sprocket is a stock 39t JT.

[gregvhen]

the new also fits flat side in. i just got a JT too.

[socialDK]

  thanks