Caps for VWR® 9 mm Screw-Thread Vials Supplier: VWR International Description: VWR* Caps for Screw-Thread Vial, color: Blue, Material: Polypropylene, Blue PTFE/White Silicone, Pre-Slit, designed with a crimp cap profile for robotic arm autosamplers but have easy-to-use screw-thread caps.