Inserts are 6" long. Initially, Mark out 14 inserts on .625in (5/8") diameter tubing. Aluminum is easy to cut. A vice provides a stable base but is not required.

 

After cutting the insert sections, use a file to smooth the edges, if needed, to allow the inserts to slide easily into the .750 ( 3/4") stringer sections. Though an inexpensive tube cutter will do the job, a heavy duty model, as shown, makes the job easier. Next, The 6in inserts will be drilled and riveted into the 6ft stringer sections.