The Null-Machining 3D Tool  

 from the interiorcad tool set can be used to insert machinings as a placeholder. Such machinings do not trigger a CNC output. They may be necessary if you want to use fittings with the interiorcad placement tools, but do not want to perform all the machinings required for the correct operation on the CNC. However some of these fittings require two machinings to operate and behave correctly.
For example, if you want to connect two parts with a screw, interiorcad requires a machining in each part. If you only want to drill the machining in the surface, because you are using a self-tapping screw, you insert a Null-Machining as a placeholder in the fitting for the machining in the edge.