Talboys 916191 Stainless Steel X-Large Column Clamp - 92mm-165mm Holding Range, 368mm Length | Heavy-Duty Pipe Fixture for Construction, Plumbing & Industrial Applications

If you are using this for any significant amount of weight you can expect the clamp to sag a bit. To counter this I just bought a second to distribute the load better. Even with a single, I was impressed at how well the welds held under the twisting and the screw clamp part has a nice easy smoothe action and has not loosened over 2 months of static use.