Stop guessing! This handy tool allows you to measure the exact size of the metric tubing you need. Simply insert the tubing or test tube over the post for i.d. measurement, or into the well on the reverse side for o.d. measurement. Polypropylene and autoclavable. Fits a range of sizes from 1.5mm to 16mm. Use for glass, plastic, or rubber tubing. Keep one gauge with tubing supplies and one with labware.