twisted metal pen holder 3d model

Create a hollow cylindrical pen holder. The inner surface must be a perfectly smooth cylinder, like a glass or cup interior. The inner diameter is constant from top to bottom and must not be intersected by any outer details. The drill-bit style twisted flutes exist ONLY on the outside of the cylinder. Outer geometry must not intrude into the inner cavity. Open at the top, flat base. Metal material. Clean, machined design.