Tractor front loaders have sometimes been provided with struts enabling them to be locked in raised position. These struts have had to be moved bodily between operative and inoperative positions. To avoid the need for bodily movement, the struts are made telescopic and are pivotable on loader support frames fixed to opposite sides of the tractor. Loader booms, and the rams of ram-and-cylinder assemblies for pivoting the booms, are pivotable on the support frames in known manner. The struts comprise inner and outer channel sections and are pivotable between retracted inoperative positions in which they are secured to the support frames and extended operative positions in which they are secured in contact with the adjacent ends of the cylinders of the extended assemblies.