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I have an O-shaped aluminum (7075) profile WxDxH - 40mm x 200mm x 25mm The inner channel is 20 mm wide and 10 mm deep - runs through the entire length of the bar.

Inside, I have a 20 mm x 10 mm bar (also Al 7075). As you can see from the attached picture, on the opposite face there's a hole in which a flat screw is used to fasten the two pieces in position.

enter image description here

This telescopic mechanism needs to withstand large loads >50 kg (>110 lbs) on both ends and I'm worried that using only a screw would mean that there will be slippage.

Is there a better way to design a secure clamp for such a telescoping mechanism? I need to be able to do fine positioning and have the confidence that it won't move.

Thanks in advance for your help.

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  • $\begingroup$ Define "fine"? a square washer or spreader plate with "teeth or corrugations or knurling" between the screw and the inner bar may work... $\endgroup$
    – Solar Mike
    Commented Aug 10, 2017 at 17:20
  • $\begingroup$ Hi, fine as in 1/2 cm increments at least. Thanks for your suggestions $\endgroup$
    – JackS
    Commented Aug 10, 2017 at 19:54

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If I were building this I would do three things to make the assembly secure, you may think it is over-kill but I will throw this out to you anyway. Where you have the threaded hole to receive the locking screw, I would have a flangemount locknut threaded insert instead. Instead of a plain screw I would use a set screw with a pointed tip that would dig in to the aluminum to give you more holding power. And last but not least , have several of these set screw assemblies spaced along the length of the tube, don't rely on just one screw to hold 100 lbs!

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