Yes, the parts slide against each other. Not a lot, but they do slide.
As they only slide a little bit, and it's roughly always the same bits
they slide on, they might develop lands, ridges, or whatnot at the ends
of the travel.
So I'd try and use materials with different hardnesses - one really
hard, one as soft as practicable - if at all possible.
The soft part should probably be in the middle, and slightly shorter
than the outer bits along the direction of slide, for best results. The
way the ends of the short soft part will be worn down by the hard part,
and no ridges should form.
Hope that's clear,
-- Peter Fairbrother
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