Borosil Amber Solid Penny Head Glass Stoppers are with Interchangeable Ground Joint and can be used with Volumetric Flask of 5645, 5647 families or for other suitable joints. Manufactured with low extractable quality grade USP Type I, 3. 3 Borosilicate Glass confirming to ASTM E438 Class A requirements. Available in sizes of 7/16 to 55/54. Amber blocks 300nm to 500nm. In collaboration with Borosil Glass Works, Foxx Life Sciences is proud to bring the outstanding quality of Borosil Type 3. 3 Borosilicate glassware to North America for the first time. Manufactured from the same USP Type I, Borosilicate glass that North American scientists have come to trust, Borosil Laboratory Glassware offers unparalleled mechanical strength, clarity, and reliability at competitive prices. And thanks to a unique annealing process, Borosil Glassware is stress-free and incredibly resistant to thermal shock.