Roller tube and roller system with such tube

The winding shaft (20) has a main body (22) formed as a cone-shaped hollow metal part along a winding shaft axis (2), where the main body is provided for receiving a coiled removable sheet (30,30a) of the winding shaft. The wall thickness of the main body is varied along the direction of the winding shaft axis. The wall thickness is enlarged from an end (22a) of the main body with a larger outer diameter towards another end (22b) of the main body with a smaller diameter. The main body is made of aluminum or aluminum alloy. Independent claims are included for the following: (1) a roller blind system with a coil spring received by the winding shaft; and (2) a method for manufacturing winding shaft for a roller blind system.