The Boveda 320 Gram Mounting Plate is used to attach the Packs to the lid of your humidor. The Mounting Plate also comes with a magnetic mounting kit and is made only for the 320 gram packs (*do not use with 60 gram packs).The 320 Gram Pack from Boveda is their largest size yet. The 60 gram pack is the most popular size but they released the 320 gram to condense 3-4 normal packs into one. Boveda says that this new release will last up to 6x longer than a normal Boveda 60 gram pack. These packs are created to fit into humidors ranging from 25ct to 150ct. The 320 Gram Pack is accurate to +/= 1% as long as they are kept in an airtight environment.