Bessey F-Clamp Ridges Worn Out

Last year I purchased two Bessey F-Clamps, recently I notice that the clamps was no longer gripping. On inspection of the vertical bar I notices that the rear ridges/thread have worn out/disappeared at certain spots. Now I was expecting to get more then a years occasional use out of these clamps. So.......



Is this normal for Bessey to wear out this fast?

Does Bessey have any warranty on their products?

Can it be repaired?