Every MEP connector in Revit has it’s own coordinate system – it’s own idea of which way is “left” and which way is “up”. In fact all 3D MEP software uses some implementation of a connector coordinate system. It’s not optional, and some do it better than others. In all Fabrication MEP products excluding Revit, the “Attacher Arrow” gives us some control over how this coordinate system is oriented.

In Revit this coordinate system is invisible and carries over from one part to the next, in MOST cases. Straights behave differently and can rotate their coordinate system at the will of Autodesk – typically whenever the Height is greater than the Width. The invisibility and inconsistency of this coordinate system makes modeling some Fabrication Parts in Revit extremely unintuitive and error prone – through no fault of the designer.

Please consider this single isolated example. The connector coordinate system of this tap simply depends on which way the “boot” is facing. This is fine for the tap, but does not necessarily make sense for connected fittings, especially transitioning fittings and offsets. The “left flat” option can become right, top, or bottom flat. Likewise, the “top flat” option can become right, left, or bottom flat. Tags become unreliable at best, and any control over which side our slip and drive connectors are on is completely lost to this behavior.

We can’t fix these issues unless our software provides us with this information. With all that said, it is my pleasure to introduce to you the “Revit Attacher”.