National Scientific 4 mL Screw-Thread Vials National Scientific Caps Case. Closures are available in polypropylene or phenolic resin. Convenience kits include vials and caps with pre-inserted septa. Preassembled kits have vials with preattached caps and septa packed in a reusable support tray. Certified vial kits are tested and certified to meet or exceed up to 17 critical performance parameters; certificate enclosed with kit. National Scientific 4 mL Screw-Thread Vials National Scientific C4015-1A Caps Case