Screw top Micro tube translucent caps only are manufactured from polypropylene. The cap contains an O-Ring that ensures a leak-proof seal and are a highly visible contrasting color. Caps are available in red, orange, yellow, green, Blue, Purple and clear. Temperature range of -196°c to 121°c. Sterilized by irradiation (SAL 10-6), RNase/DNase free and non-pyrogenic. Every case is printed with the lot number for quality traceability.