I sent the Benbo back and requested a replacement. There’s a lot to like about that tripod IF it will just lock down when deployed close to the ground, so I’m going to give Benbo another chance and see what happens. If the second sample has the same problem as the first, I’m going to go to plan B, return the Benbo and get a Vanguard. Hopefully, that will not be necessary.
Sorry to read this, have't been on the forum for a few days much.
I have just tested my Benbo tripod out of curiosity. I set the height to about 6inches, 150mm under the knuckle then tightened the clamp to 20 Lb/Ft or more modern equivalent 27 Nm. A normal mild steel ISO 10mm bolt should easily withstand 30 Lb/Ft so by no means over tightened. As tight as I can comfortably tighten it by hand with the standard handle.
I then placed a dial gauge indicator (DTI) on the knuckle. I applied 10Kg force down on the centre post which resulted in just over 70 thou deflection, on release the DTI returned to zero. I went on to press down on the centre post until I had almost half an inch deflection registered on the DTI when I released the pressure the DTI returned to about ten thou less than zero, so it might have slipped a smidgins but more likely the carpet was crushed! Bear in mind this wasn't scientific, it was on carpet and my measurements aren't 100%. I don't know how hard I pressed down on the centre column but it must have been between 40 and 50 Kg. I still have the indentation in the palm of my hand from pressing it down.
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Two thoughts pass my mind, firstly you are being too cautious tightening the handle, secondly the new tripod paint may have lower friction coefficient than the paint on mine, what's left of it... From day one I have tightened the handle as tight as I can, if needs be, it was many years before the threads stripped and then, not suddenly. The repair was cheap and actually better than the original, so nothing lost, just stronger and longer lasting.
Incidentally, the red tape on one leg is to remind me which lower leg comes right off, if stuck for a monopod I use that leg together with the centre pole as a short monopod if the need arises.