Abstract: A device includes a melt feeder with an outlet opening for discharging a glass melt and a shaping mandrel having a shaft and a shaping body. The shaft extends through the outlet opening forming an outlet ring between the shaft and a circumferential edge of the outlet opening so the glass melt can flow through the outlet ring and over the shaping body thereby forming a hollow glass drawing strand. The shaping body has a first part extending from a lower end of the shaft in an axial direction along a length X and having a conical outer surface, and a second part extending from a lower end of the first part in the axial direction along a length Y and having a cylindrical outer surface with an outer diameter Z. A ratio X/Z is between 0.1 and 0.5 and a ratio Y/Z is between 0.02 and 0.35.

Abstract: A glass tube has a center axis, where for the glass tube a specific cross-sectional plane is defined which includes the center axis and which is parallel to the center axis. Within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected first axial position x1 and second axial positions x2 along the center axis, respectively, the following relation is 60 or smaller: |(d2?d1)/(x2?x1)|*(10{circumflex over (?)}6 mm)/d1.

Abstract: A glass tube has a center axis, where for the glass tube a specific cross-sectional plane is defined which includes the center axis and which is parallel to the center axis. Within the specific cross-sectional plane, for each pair of outer diameters d1 and d2 of the glass tube at any two arbitrarily selected first axial position x1 and second axial positions x2 along the center axis, respectively, the following relation is 60 or smaller: |(d2?d1)/(x2?x1)|*(10{circumflex over (?)}6 mm)/d1.