A telescopic boom includes a first frame having a curved portion whose section is substantially U-shaped, and a second frame connected to the first frame so that a closed section is formed. In the telescopic boom, the U-shaped curved portion of the first frame includes a plurality of protrusion portions formed at intervals in a circumferential direction of the telescopic boom, each protrusion portion extending in a longitudinal direction of the telescopic boom and being formed to have an arc-shaped section and protrude to the outside of the first frame.

The invention relates to a collar bearing for a telescopic boom for the sliding support of two telescopic sections in the collar region of the outer telescopic section, wherein the collar bearing includes fixing means, whereby the collar bearing selectively is releasably connectable with the outer or inner telescopic section.

A crane includes a crane pillar rotatably mounted about a vertical axis, at least one jib, connected to the crane pillar and pivotally mounted about a horizontal axis, at least one jib extension movably mounted in the jib, and at least one piston-cylinder unit for extending and retracting the jib extension relative to the jib. The first end of the piston-cylinder unit engages the jib via at least one first force-introducing region, and the second end engages the at least one jib extension via at least one second force-introducing region. The piston-cylinder unit has a central plane parallel to the horizontal axis about which the jib is pivotally mounted, and the piston-cylinder unit has a compressive deformation perpendicular to the central plane in a pressure-loaded state while the jib is being extended and a tensile deformation opposite the compressive deformation in a tension-loaded state while the jib is being retracted.