Each of said elongated objects comprises a body and a flange. The tray includes a plate with openings and bearing surfaces.According to the invention: the tray includes at least one first bearing surface near a first opening, located at a first distance from the plate of the tray, and at least one second bearing surface near a second opening adjacent said first opening located at a second distance from the plate of the tray, said second distance being different from said first distance; said first and second openings are located at a distance one with respect to the other such that the flange of the object engaged in one of these openings is able to partially overlap the flange of the object engaged in the other of these openings without contact with this flange.