12mm Clear Polyethylene Starburst Conical Snap Plug. Our Glass Shell Vials have straight sided walls for maximum labeling space. Our shell vials are made from sturdy, chemical and thermal resistant type I borosilicate glass. Seamless, tubular, glass shell vials are often used for sample analysis for chemicals, specimens, and other materials. Shell vials play a particularly integral role in viral cultures. All standard shell vials are for use with corks. The 1 dram and 4 dram shell vials can use plastic stoppers as well.