Apr 08, 2021 · Snap Top Vials Snap Top Vials are convenient for lab technicians and are sometimes preferred over screw thread vials. Snap Top vials are typically used for HPLC or LCMS analysis, and the closure is simply pressed down on the vial to make the seal. Step 2: Determine Volume of Vial. 2mL Autosampler vials are the most common vial type.