[Stocker]

As I recall, loosen those three small allen screws. Then rotate the threaded collar counterclockwise by hand to remove it. If it's too tight to rotate by hand, insert a screwdriver tip into one of the holes and tap on in to break the collar loose. Shouldn't take much. There's a multi-slotted tabbed washer behind the collar, and those allen screws extend into the slots to prevent the collar from backing off.