Instance Length Parameter with Grips

I was recently asked about instance parameter grips for a Revit family that was placed in a Revit project file.  The family had an instance parameter in it for a dimension and the user was expecting to see grip arrows so that they could manually adjust the size by dragging the grips.  The arrow grips did not exist and the user was curious why that was the case.

The answer to the user’s question is actually very simple.  When creating a dimension that will be referencing an instance parameter, it is important to dimension between two Reference Planes for the grip arrows to appear.

The following illustration shows how the instance parameter is desired to look by showing the grips in the project file.  In this illustration, the dimension goes between two Reference Planes, including the Reference Plane below the box which is in the same location as the Ref. Level.

The following illustration shows how the family looks when the instance parameter does not show the grips in the project file.  In this illustration, the dimension goes between a Reference Plane above the box and the Ref. Level below the box.  (Note that it is difficult to tell just by looking at the family whether the dimension goes to the Reference Plane or the Level in this situation.)

Some common situations where the arrow grips do not appear when desired include:

• One end of the dimension goes to the Ref. Level line instead of the Reference Plane.
  • This is common since a Reference Plane is at the same location as the Ref. Level and it is easy to accidentally pick the Level line instead of the Reference Plane.
  • When dimensioning in this situation, press the Tab key until the Reference Plane is highlighted.
• One end of the dimension goes to a wall face instead of a Reference Plane.
  • This is common with doors, windows, or other items that are hosted in a wall and you have a dimension (controlled by instance parameter) which goes to the face of the wall.
  • In this situation, create a Reference Plane at the face of the wall and lock the Reference Plane to the wall face.  This Reference Plane can then be used for the dimension.

While it is not required to always dimension between Reference Planes to get the grips, it is good practice to always create Reference Planes in a family and dimension to them instead of line work, extrusions, etc.

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