The accompanying engraving illustrates a selfdocking double dovetail which cannot be pulled off in either direction. On one of the pieces the tenons are chamfered at the inside while the grooves on the other piece are formed with a correspondingly chamfered inner wall. The corners are joined not by forcing one side piece at right angles to the other, but by placing the side pieces within the ends of the end pieces and then bringing the corner joints into place by moving the side pieces diagonally outward. A box thus constructed cannot pull apart without first crushing in the sides, as this is the only direction in which the tenons of the side pieces may be moved out of engagement with those of the end pieces.

Fig. 93 - The self-locking dovetail joint.