Cvtimo

I've just bought a 2000 RX300 that has a roof rack (not after market) that needs the 2 bars reattached. There are sliding pieces into which the ***** screw, and a rubber square that seems to be part of the set up.

Can anyone tell me:
1. How does the rubber square fit into the equation?

2. What's the right orientation for the slider piece? I.e. Does it matter which end of the piece faces forward? (it seems that the slider piece only fits in smoothly one way in terms of "heads or tails" if you know what I mean...)

Thanks!