Keys, Tongues and Slip Feathers
From DT Online
In Cabinet Making, and other forms of fine woodworking, Keys, Tongues and Slip Feathers are terms used (sometimes interchangeably) to describe small pieces of material (usually wood) which are used to strengthen a joint. they can also be used to create a decorative effect if a contrasting colour material is used.
If a contrasting wood veneer is used and/or the directions of the saw cuts varied, some interesting decorative effects can be created.
Thin strips (or Slips) of Ply, timber or other materials can be inserted into a Groove cut into each joining face to form a Loose Tongue which completes the joint.
If the strip is made from timber, its Grain should run across the joint (i.e. in the direction of the arrow) to achieve maximum strength.
Shaped Keys and Tongues
Small pieces of contrasting wood or other materials can be shaped and inserted into matching recesses to produce bold decoration in addition to adding substantial strength to the joint .