A spirit level is provided which may be conveniently packaged and sold in knocked down form with the liquid vials and vial holders initially separated from the frame. The mounting openings in the web of the frame are rectangular or square with sides parallel and perpendicular to the working surfaces of the frame. The vial holders comprise a pair of opposed mating members of complementary configuration with the opening and having four pairs of mounting tabs for positioning the vial in accurate parallel or vertical orientation by cooperating with the corners of the rectangular opening. The holders also comprise posts which cooperate with the pairs of tabs to urge the tabs into gripping engagement with the corners of the mounting openings.