Wide neck flasks allow easier removal of viscous or solid samples and enable the use of the anchor and propeller style PTFE stirrer blade options. These unique vessels feature a 50mm ID flat flange which combines with a nitrile O-ring and our unique self-centering PTFE collar to offer a leak-tight seal between the glass flask and wide neck reflux tube. The two flanges are compressed together using a two-part threaded polymer coupling, which holds the components rigid and sealed.