A mitre joint (often miter in American English) is a joint made by cutting each of two parts to be joined, across the main surface, usually ...
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at a 45° angle, to form a corner, usually to form a 90° angle, though it can comprise any angle greater than 0 degrees. It is called beveling when the angled cut is done on the side, although the resulting joint is still a mitre joint.
For woodworking, a disadvantage of a mitre joint is its weakness, but it can be strengthened with a spline (a thin wafer of wood inserted into a slot, usually arranged with the long grain of the spline across the short grain of the frame timber). There are two common variations of a splined mitre joint, one where the spline is long and runs the length of the mating surfaces and another where the spline is perpendicular to the joined edges.