The Conklin Sherman Company   Adjustable plug has been tested to: 100-125 PSI   Very Important - Plugs must be properly installed in a clean dry tube   Plugs must be the right size   Shelf life of plug is 2 years if stored in a cool, dry area   Rubber is nitrile (Buna N)   Rubber is oil resistant and can take temperatures up to 260 degrees Fahrenheit   Metal insert is all brass   Each Conklin Sherman adjustable plus is 100% inspected   Adjustable plugs can be reused many times   Other rubber compounds are available. Please ask us for more information.