You can use a screw that goes through both inner and outer tubes to keep them in place. With some smaller aircraft, especially gliders, you can simply use friction. There''s not a lot of spanwise load on a mode, so anything that can keep the wings from sliding out will work. I''ve had gliders that used a rubber band between two hooks that held the wings in place...the hooks were in the root ribs of the wings, and the rubber band stretched across the fuselage between the hooks.

Many ways to do the job.