Premium Borosilicate Glass Dropping Funnel Open top, cylindrical shape 250 ml capacity fitted with PTFE key stopcock Great for controlling the flow on fluid transfers that require a high degree of accuracy. 2.13" diameter with a 13" length This premium quality dropping funnel allows the user to add reagents slowly, one drip at a time. The funnel is fitted with a PTFE stopcock that allows maximum control over drip rate to prevent reactions that may occur if the reagent is added too aggressively. It has a 2.12" diameter and is 13" tall. The interior diameter of the spout is .25" and it measures 3" from the stopcock to the end. Eisco Labs Borosilicate glass has the following heat tolerances: Strain Point -515°C | Annealing Point 565°C | Softening Point 820°C.