I want to design an extendable pole made from aluminium alloy circular cylinder and an extendable alluminium alloy circular bar which slides in and out. To clamp i wish to turn a thumb screw located at one end of the tube and passes through the bar. It relies on deforming the tube walls to clamp against the bar. But what forces and stresses am i particularly concerned with? How is it possible to calculate the clamping force from certain dimensions? How can i be certain a cylinder wall of a certain thickness will not yield? Any help would be very much appreciated. And directions to sources I should read would be particularly useful. Thanks again.