These Erlenmeyer style flasks are manufactured from heavy-wall borosilicate glass to assure the mechanical strength needed for vacuum filtration. For added safety, plastic safety coating is chemically bonded to the glass. The plastic safety coating is steam autoclavable to 135°C. The 125mL flask has a No. 5 stopper joint. The 2 and 4 liter flasks have a No. 8 stopper joint. All flasks have a #2 side arm for connection to 1/4" (6 mm) I.D. flexible tubing.