Cylindrical shaft, transport roller, transport unit, and printing apparatus

A transport roller comprising:

• a cylindrical shaft having a joining portion, the joining portion extending between one axial end of the cylindrical shaft and an opposite axial end of the cylindrical shaft;
• wherein the joining portion includes:
• a central linear section which is provided on a center portion in an axis direction of the cylindrical shaft wherein the central linear section is formed in a linear shape extending to the axis direction;
• and
• a projection part provided outside of the region of the central linear section and projected in a direction which crosses a direction along which the central linear section extends,
• wherein the projection part includes a circumferentially extended portion and a corresponding circumferentially recessed portion that interleave,
• wherein a surface of the circumferentially extended portion contacts a surface of the corresponding circumferentially recessed portion in a side portion of the projection part,
• wherein all of an edge portion of the projection part in a direction of rotation of the transport roller has a gap,
• wherein a spacing of the central linear section is wider than a spacing of the side portion of the projection part.