The machine tool shop where I worked years ago used to do this: The square tube had a weld seam running the length of the inside of one wall. Rather than trying to get rid of the seam, they would mill a channel along the outside of the inside telescoping tube.
Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
~Practitioner of the Electromechanical Arts~
Theory & Practice-
Theory is when you know something but it doesn't work.
Practice is when something works but you don't know why.
It it dangerous to combine Theory & Practice;
nothing works and you don't know why.