This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The mortise for this joint is made in the usual manner, the only requirements being that the mortise is run through the piece, and the tenon is cut 1/8in. shorter than the depth of the mortise or the width of the piece it is entering. The end of the tenon and the mortise is then covered with a piece of metal, fastened with screws as shown. The metal can be of any desired material and beveled on the edges. This makes a very good knockdown joint for mission furniture. - Contributed by H. R. Allen, Cheyenne, Wyoming.
Ill: Metal Covering and Holder for a Tenon and Mortise Joint on Mission Furniture