Fits two structural members together in a miter joint.
 Ribbon: Structure tab 
 Cutting panel 
 Miter Cut Member
 Command entry: 
plantsteelmiter
The following prompts are displayed.
Click a structural member or enter an option.
Select a first and second structural member to align cut edges. Repeats so you can cut multiple objects.
Specifies the gap of the miter cut. You can specify a distance or enter a positive value.