48PK Test Tubes, 20mL, 16x150mm - Rimmed - Light Wall, 1.2mm Thick - Borosilicate 3.3 Glass

This 48-pack contains heavy duty borosilicate 3.3 glass test tubes with a 20mL (0.7oz) capacity and uniform 1.2mm walls. Each tube measures 5.9 inches (150mm) tall with an outer diameter of 0.63 inches (16mm) and an inner diameter of 14.8mm. The tubes accept stoppers with a bottom diameter of 13 to 14mm and a top diameter of 17 to 18mm. The rims are fire polished into a bead rather than cut. Fire polishing rounds the glass edge under heat and removes the microscopic flaws where cracking begins, producing a rim that resists chipping through repeated racking and washing and giving a stopper a defined seat. Uniform wall thickness prevents thermal stress concentrating at a thin point, which is the common failure mode over a burner. Borosilicate 3.3 glass withstands direct flame, high temperatures, and thermal shock, and the tubes are autoclavable for sterilization and reuse.