The mitre joint is one formed by the meeting of two pieces at a corner, on a line bisecting the right angle. The same class of joint may be used on angles greater or less than 900, as in Figs. 31 and 32. The mitre joint is extensively used in door and window making, joining of architraves, picture frames, and all sorts of mouldings. It is also much used in cabinet and pattern making. Keying is a process sometimes employed along with this joint to strengthen it. A saw cut is let in as far as the dotted line on Fig. 30, into which is glued a thin slip of wood. If it is a deep joint, as the corner of a box, a few keys may be put in, as shown in Fig. 33, while in a small picture frame, only one would be used. A mitre square, i.e., one set at the angle of 45°, is used for drawing on the lines for this joint. When much work of this sort has to be done, as is the case in picture frame making, etc, a mitre-box is used. These assume many different forms, some for the use of the saw only, and others with the addition of a knife to finish the joint, or adjuncts for the application of the plane after sawing.