Sigg WMB Adapter - leak-proof cap for drinking bottles. The Sigg WMB Adapter is the perfect addition for all Sigg drinking bottles with a wide mouth opening. This allows any Sigg cap designed for narrow mouth bottles to be used on all wide mouth drinking bottles. Additionally, the practical screw cap is always airtight, ensuring that the drinking bottle is guaranteed to be leak-proof. The screw cap is, of course, BPA-free and contains no harmful substances, including phthalates or estrogen-active compounds.