These Pyrex® Squibb pear-shaped separatory funnels have PTFE PS stopcocks and ST polyethylene stoppers. The stopper is made with a closed bottom and is of linear high density polyethylene to conform to ST stopper dimensions. The PTFE plug fits into the micro-finish barrel. The plug also reduces freezing problems and grease contamination. For replacement polyethylene ST stoppers, see Cat.No. 1-7624; for PTFE stopcock assemblies, see Cat.No. 1-7681.