Inserts are placed directly into the host vial for small-volume sampling. The 1.2 ml shell vial insert (8 x 42 mm) fits directly into the vial. The 300 ul (6 x 39 mm) tapered glass and 250 ul (6 x 35 mm) tapered polyethylene inserts require a spring for support; the spring is reusable. TriSpring inserts have a plastic support spring permanently attached. 300 ul capacity. The plastic spring centers the insert in the host vial and acts as a shock absorber to prevent needle damage. These are available in either glass or polypropylene.