At least one glass tube has an azimuthal wall thickness deviation WTD of not more than 6.0%, the azimuthal wall thickness deviation being determined based on a lowest wall thickness value and a highest wall thickness value measured within a cross-section of the at least one glass tube, the azimuthal wall thickness deviation WTD being calculated according to the following formula: W ⁢ ⁢ T ⁢ ⁢ D = 100 - ( lowest ⁢ ⁢ wall ⁢ ⁢ thickness ⁢ ⁢ value highest ⁢ ⁢ wall ⁢ ⁢ thickness ⁢ ⁢ value * 100 ) ⁢ ⁢ % .