The Break command enables you to break (remove part of) an object by defining two break points. In the illustration below, a corner of a rectangle has been removed. The Break command can be used with lines, polylines, circles, arcs ellipses, splines, xlines and rays. When you break an object, you can either select the object using the first break point and then pick the second break point, or you can select the object and then pick the two break points.
Select objects: (select the object using the first break point, P1)
Specify second break point or [First point]: (pick the second break point, P2)
The section of the object is removed and the command ends.
Sometimes you may want to select the object first and then specify the two break points. If this is the case, use the "First point" option to specify the first break point. By default, AutoCAD assumes that the point used to select the object is the first break point. This is often confusing for new users.
It may sometimes be necessary to break a line into two without removing any part of it. In this case, simply pick the first and second break points in the same position.