Booms are fixed to a rotating or non-rotating base. They exist as one extended arm or articulate with two or more hinged sections. Some booms are capable of telescoping to different lengths, while others have one fixed length.
They are most often controlled hydraulically.
Different types of booms include: the offset boom, which is offset at the connection between the boom and the stick, enabling it to work very close to structures; the swing away boom; the variable angle boom, which is comprised of two pieces and can be hydraulically adjusted; and the two-piece boom, with two pieces that must be manually adjusted by changing the pin settings.