What is (a) A long piece of timber, forming a margin or edge of any piece of construction; esp.: (b) One of the longitudinal pieces, supporting the treads and rises of a flight or run of stairs called?

stringpiece — (a) A long piece of timber, forming a margin or edge of any piece of construction; esp.: (b) One of the longitudinal pieces, supporting the treads and rises of a flight or run of stairs. (Webster's 1913.)

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