The provisional cast on is often used in situations where you want to knit in one direction, then pick up your stitches (at the cast on edge) and knit in the opposite direction. However, this cast on can also be used when you want to create a stretchy edge for fabric with 1 x 1, or k1, p1 ribbing.
The provisional tubular cast on creates an edge that looks like your 1 x 1 ribbing invisibly flows over the edge from one side to the other. The cast on works for pieces that are knit flat, back and forth, in rows or in the round.
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