These microculture vials feature deep-skirted screw caps to allow safer, more dependable handling when working with infectious materials. Solid-top black phenolic caps have a white 14B rubber liner and can be autoclaved. Vials are packaged in corrugated trays with partitions. Manufactured from Wheaton 33 low extractable borosilicate glass (meets ASTM Type I Class A and USP Type I standards). The 4mL size fits M-T Vial File® 12-228780.