Not quite a year ago Amazon had a good deal on Bessey Kliklamps, about half price. I ordered 4 and have used them a lot.
Fast forward to 4 months ago and most of the clamps will not hold their grip. The movable clamping section cannot grip the shaft tightly enough to keep from slipping.
An e-mail to Bessey was answered with the suggestion to use lite steel wool on the shaft and wipe the shaft down with a clean dry cloth. That WORKED, for about 3 weeks. I repeated about 3 times again but the remedy was always short lived.
Another email to Bessey was answered with the suggestion that they send me 6 replacement clamps and I send the 4 in question back to them at my expense. I am $$ ahead and hopefully the new clamps have addressed the matter.