A holder carried on an agricultural tractor for holding implement coupling balls (1,2). The holder has a rear wall (3), two side walls (4), a base (5) and an open upper end through which the balls may be inserted into the holder. The side walls (4) are shaped (4b) to retain the balls (1,2) within the holder with the inside surfaces of the side walls in contact with portions of the spherical surfaces of the balls which face away from the rear wall (3), and bias means (8) are provided for biasing the balls (1,2) into contact with the inside surfaces of the side walls. An adaptor element (10) may be provided for partially enclosing a ball of a smaller category than the holder was designed to hold, the adaptor element being positioned between the smaller category ball and the side walls (4) so that the smaller ball and adaptor element together occupy a similar volume to the volume occupied by a ball of the category which the holder was designed to hold.
