Wheaton screw caps black, 22-400 with ptfe /14b rubber liner. Black phenolic screw cap ptfe faced (14b) styrene-butadiene rubber liner provides totally inert inner seal and surface facing the sample or product designed for the ultimate in product safety autoclavable. Warning: this product can expose you to chemicals including tetrafluoroethylene, which are known to the state of california to cause cancer. Prop 65 warning