Leather roach bases are designed to match the shape of the back of a War Bird face. They are cut from from heavy tooling leather and accept hot melt glue very well. We use them to attach multiple beards and decorative hair, to resemble the native ceremonial roach.
You can see how we have used  multiple Jake beards, as well as long beards on others,  I prefer to 'hammer' or flatten the beard base first before gluing to the leather. When all your beards are attached , just hot melt glue to back of the finished War Bird face. You can always  add more beards at later times. 
 
 They measure app. 7 1/2 inches along the curve.