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.

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Flexible 3-Point Arc in Revit Family

Occasionally, you need to create an arc in a Revit family and you know 3 points of the arc, but not necessarily the radius, and you need it to be flexible.  It is common for windows with a radius top to have this situation.  You know the chord length (width of the window) and the distance from the top of the straight sides to the top of the window arc, but not the radius of the arc.  Revit requires you to specify the radius and center point of the arc to allow it to be flexible, so it is important to determine that information.