Screw Top. MicroAnalytix NZ provides a variety of HPLC & GC Vials products, Vials, UniPrep Vials, Crimp Top, Dram Vials, Headspace Vials, Pre-Assembled Vials, Screw Top, Shell Vials, Snap Top Vials Screw thread vials come in various neck sizes 8mm, 9mm and 10mm. Designed to work in a variety of autosamplers requiring narrow to large neck vials.