Consider two pieces of square steel tubing, one 5", one 4",
both 1/4" wall thickness (these are hypothetical, not real).
...snip
This is the principle of how the telescoping boom on my knuckle
boom truck works.
Grant Erwin
Grant, That's an interesting idea; I wondered how those booms
were spaced internally.

How / what lubrication is used on those booms??

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?