For use with Buchner Funnels as an alternative to boring a large hole in a rubber bung. The seal between the Buchner funnel and flask forms around the tapered base of the funnel and not the stem. It is therefore necessary to select a cone that fits the neck of the flask and not the funnel stem. Int. 20/14 Ext. 26/19mm for Flask Neck 21. Priced in single units.