Keystone - Wooden
A keystone is pounded into the cask (firkin) top (outlet) before being tapped. The keystone is pre—scored to allow the tap to drive into the cask. A benefit of wood over a plastic keystone is its moldability to the firkin opening. Quite often through use the opening in the firkin is damaged and mis—shapen and the wooden keystone is able to mold itself to the opening.