Abstract: A multi-section telescopic jib or boom comprising a base section and three movable sections mounted to extend or retract relative to each other on operation of drive means within the sections, including a first ram connected between the base section and the innermost sections, a second ram connected between the innermost and central sections and a chain having ends connected between the innermost section or the first ram and engaging a chain wheel mounted on the central section or second ram, means being provided to releasably connect the chain to the outermost section to extend the boom.