WHEATON® W224215 Pressure Release Aluminum Seals, 20 mm, PTFE/Silicone Septa (20 mm Headspace Seal, Alum, Press Release) These 20mm seals are special crimp top closures with bridges and score lines in the aluminum seal. This design is an added safety feature, allowing the internal pressure to be released when 3.0 +/-0.5 bar has been exceeded.