Disposable Borosilicate Glass Snap Cap Centrifuge Tubes are made from borosilicate glass in compliance with ASTM Specification E438, Type I, Class A or B glass requirements. With conical shaped bottoms on the 5, 10, and 15 mL sizes and a bullet-nosed shape on the 50 mL size to withstand centrifugation up to 2980 RCF. The 5, 10, and 15 mL sizes have a finished top for a snap-cap closure. Tubes are plastic shrink wrapped in modular trays to keep them clean and safe in transit. Snap-cap closures are not supplied.