The FILLET command fillets and rounds the corners of objects. If you use this command to connect 2 objects and set the fillet radius to zero, the command trims or extends the objects until they intersect but does not create an arc.
In AutoCAD MEP 2023 toolset , you can use FILLET to fillet not only AutoCAD objects, such as lines, polylines, and arcs, but also schematic lines and plumbing lines. By using FILLET with a fillet radius of zero (default), you can easily connect schematic lines or plumbing lines by extending or trimming them. You can use the command in orthographic mode or isometric mode.
Filleting plumbing lines
Note: The resulting single schematic line or plumbing line has the properties of the segment that you select first, such as system, style, and flow direction. In the case of plumbing lines, the resulting plumbing line also has an elbow of the type specified for the plumbing system. For more information, see Specifying Default Fittings for a Plumbing System.