Usually straight sections are 10 feet, but they certainly do make other lengths, top sections can vary as do base sections.
To me, it appears to use the type of base that gets buried in concrete as shown in the drawing below. I have also seen installs where they just buried the first couple feet of a standard straight section for a base.
Anybody pursuing something like this should be prepared to cut and grind flush anything protruding from the concrete, as well as have the homeowner fully agree to your well outlined course of action.
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