David, the rubber piece is a "T" shape piece of vinyl. The top of the "T" slides into the track, and Sam's has that piece. It works OK, but there is a lot of room for improvement. I have one shower door that opens inward and I could not for the life of me get that shower door to stop leaking. I eventually made my own water trap for that one using a large vinyl strip - not pretty, but it got the job done.
As luck would have it, I just pulled a piece of this out of my truck last weekend or so to replace the strip in my crew shower. Below is a picture of it.
On another note, has anyone replaced these shower doors instead? Mine are a little cruddy and I have small spots where the aluminum is corroding. I think I'd like to have a bi-fold door for the smaller showers I have as that would make maneuvering around them in the small space a little easier for everyone. They are just slightly smaller than a standard "small" shower door which makes replacing them a bit of a difficult find, short of a full-blown expensive custom job. My doors aren't in that bad of shape to warrant that yet.
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