When you select 'Strut' on the Isolate tab and click on a strut, the following dialogue appears:
NOTE: Option two, “Length of strut’s center line”, is disabled for Face Type struts.
Which length option you choose for deriving the Isolate set will depend on your own particular design and production process (eg how your mitre-saw is configured, etc). You may calculate the strut length as any one of the following:
A. Length of original quad-edge
The length of the strut is considered equal to the length of the underlying quad-edge (ORG to DEST). The figure below shows a strut (cyan) and two hubs (yellow) on the quad-edge lattice (white). There is no hub intersection, and the strut is the same length as the underlying quad-edge.
B. Length of strut’s center line.
After performing a hub intersection, the strut has been shortened to the intersections of its center line with the hub walls.
C. Length of strut’s outermost edge (as seen from the system center).
After performing 'Project strut ends to Hub Intersection Plane', the strut end is projected onto a plane that is parallel to the hub normal:
IMPORTANT. The consequence of using different lengths for Isolate Struts and Isolate Edges is that when 'Project strut ends to Hub Intersection Plane' is ON, the unique set for Strut meshes will differ from the corresponding unique set for quad-edges. Not only that, but the number of unique elements will increase. This is to be expected, even with a spherical envelope, because the angles at which struts join hubs varies over the sphere. Sometimes it is best to cross examine the two sets ( [edge] and [strut] ); if the Strut set contains two groups with almost exactly the same length values, you can fine tune the precision output in the preferences to reduce the size of the set.