Drive shaft blocks

In the past week or so I have seen the same basic comment about the little blocks on the drive shafts of locos not being squares but rectangles. I have to say it was news to me. :tb-shocked:

What is the proper way to put them back in to the loco?

1. The grooved side towards the frame sides?
2. The grooved side up and down?

They seem to fit either way.

 

I bought them from Atlas to use and when I mic. them they are the same both ways.