Franco addressed an issue with the clamp set up on another thread, here is what he posted;

YES, THE FIRST BATCH OF BISHOPS WENT OUT WITH A KNOB SCREW THAT WAS ORIGINALLY MEANT TO BE COMBINED WITH A CLAMP. SOME PEOPLE HAVENT GOT THE CLAMPS AND THAT IS WHAT THE ISSUE WAS. THE KNOB SCREW CRACKED THE PLASTIC TUBES WHEN CLOSED TOO TIGHT. IF ANYONE NEEDS THE CLAMPS OR KNOWS SOMEONE WHO DOES WHOM PURCHASED AN EARLIER MODEL PLEASE PASS OUR EMAIL TO THEM AND WE WILL SEND OUT FOR FREE OF COURSE. [email protected]
Anyway, as posted above email him and he'll sort you out.