A carrier arm 112 for an agricultural machine or tractor includes a base part 120 and an extending part 122 located partially inside the base part and extending telescopically therefrom. Upper and lower inclined bearing surfaces of the base and extending parts interact to allow the parts to slide. The inclined surfaces may be at an angle of between 30 and 60 degrees. Preferably, one of the bearing surfaces has a layer of bearing material. There may be a suspension system for suspending an operating unit from the carrier arm. The suspension system may comprise a bracket 126 and four rods 128, 130, where one pair of the upper or lower rods diverges and one pair converges. Preferably the arm is pivotally mounted by a mounting structure 114 to a vehicle. Preferably, the agricultural machine is a mowing machine, and the operating unit is a cutter unit (fig 1).
