These 500 mL PYREX® kettles have covers with four openings to accommodate 24/40 Standard Taper joints. Interchangeable Standard Taper joints allow quick assembly with condensers, stirrers and funnels. Flanges of covers and bottoms are finely ground for a tight seal. For use with heating mantle only. For replacement covers, see No. 6947-500CO: for replacement bottoms, see No. 6947-500BO.