These PYREX^® pear-shaped glass separatory funnels have PTFE (Polytetrafluorethylene) Product Standard stopcocks and Standard Taper polyethylene stoppers. The stopper is made with a closed bottom and is of linear high density polyethylene to conform to Standard Taper stopper dimensions. The PTFE plug fits into the micro-finish barrel. The plug also reduces freezing problems and grease contamination.