There are pins in the top cords of the fly that you remove and and reinstall in a certain location depending on what degree of offset you are putting in. There's a diagram on the side of the fly as to pinning location for different offsets or also in the cranes manual. The "free floating shafts" he talks about allow the pinning lugs on the boom to rotate to accommodate the change in angle of the lug needed for the offset. This is why it's important to have the shaft retaining pins removed once the jib is installed even if you're not putting an offset in. When you load the jib with weight those shafts need to be able to rotate freely as the jib deflects under load. If you do not remove the shaft pins it will damage the shaft and boom head parts and will need to be replaced. If you don't remove the shaft pins when attempting to put an offset in, the pins will not allow change of the fly lugs therefore the fly will not go into offset. I've heard of people lashing the fly off to a telehandler and forcing the fly into offset.. bad news for that guy. Very expensive mistake and was looking for a new job the next day. You can either block up under the fly to remove tension from the offset pins or use a telehandler with soft chokers on the top cords to support the fly in order to remove/install the offset pins. It's important to read the manual for proper procedures before attempting to erect or stow a jib. If you miss a step you could damage the crane or kill someone.

@@Brian_P thank you