HI steve - re: "seam of the circle" - that's referring to the starting and ending point of the circle. A closed curve is formed basically the same as an open curve, just with the ending point of the curve touching the starting point of the curve.

The particular location of that start/end point will then have an influence on the similar seam edge of the closed tube that is then generated.

Just like a closed curve has the start and end on the same point, a surface that is closed in one direction like a tube or a cylinder has a "seam edge" where 2 edges of the surface come together.

- Michael