What direction does the brass tube spacer go?

I always put my with the flanged end to the bottom -- ie: I insert them from underneath.

I do this so that the sharp (unflanged) end doesn't bite into the servo-rails and allow the gromets to be over-compressed. By doing it with the flanged end to the bottom, the washer on top will bottom out on the brass insert and limit the amount of compression applied to the grommet -- thus ensuring that there's always a reasonable degree of vibration and shock isolation.