The Secure 33 Series™ NMR tubes are made from ASTM Type I Class
A borosilicate glass ("low expansion" borosilicate glass such as
Corning Pyrex® 7740 or equivalent) and match the properties of the Select
Series™ NMR tubes from Norell. Because of the low coefficient of thermal
expansion, Secure 33 Series™ NMR tubes show a high degree of thermal shock
resistance, a necessary attribute to prevent breakage when large temperature
variations are expected in variable temperature studies, degassing samples
through freeze-pump-thaw cycles, etc.