Heavy wall cylindrical vessels have an internal thread for use with a 15mm Teflon bushing as a pressure seal. This unique design allows hand tightening and loosing for easy access into the vessel. The O-ring is positioned on the bushing above the thread for improved sealing. The vessels are useful for pressure reactions and applications such as polymerization and analysis of halogens by thermal decomposition in the presence of lime. Complete apparatus is supplied with vessel, Teflon bushing and Viton O-ring.