Abstract: A die, in which is to be formed a hollow article having a part-circular portion, such as a "J-tube", includes two opposed die blocks each formed with die cavities which together form the article, and a part-circular core which is positioned within the cavities to form the part-circular portion of the article. The part-circular core is removed from the article, after one die block has been removed, by rotating the core about an axis through the center of the part circle and raising the core along the axis. The axis is inclined to the surface of the die block, towards that length of the part circular core which emerges first from the part circular cavity.