I am new to SolidWorks, but I have some experience with FreeCAD, so I have some understanding of parametric object modeling.  

I downloaded a bundle of SolidWorks files of an extruded aluminum bar provided by a vendor, from this page.  I'm going to cut this bar into parts of different lengths, so I wanted to create multiple part files from this starting point.

I opened the SLDPRT file provided. I used