The square root angles are used where it is necessary to eliminate the fillet. The cover angles are for use in splicing so that the covers will fit the fillets of the angles spliced. As the demand for such is limited in any particular piece of work, it is customary to plane off a regular angle. The other shapes are for special uses, as will be readily understood.

Bent plates are very commonly used in place of obtuse angles. None of the above can be obtained easily at the miiis, and would be used only when it is not possible to adopt the regular shapes.

With the above explanation the student should be able to understand readily the features of the other shapes by carefully studying the cuts.

Plates are of two classes known as "sheared" plates and "universal mill" or "edged" plates. Plates up to 48 inches in width are in general universal mill plates. This term applies to plates whose edge3 as well as surfaces are rolled, thus insuring uniform width. Plates above 48 inches in width have their edges sheared, and are known as sheared plates.

As already stated, there are various meanings of the terms "beam" and "girder," and it is very important to understand fully the distinctions. The definitions previously given are applied to the manner of loading.

"Beam" is also the term applied to the shape rolled in the form of the letter I, in distinction from the channel, as noted in the preceding paragraphs. An I beam may be used in a position which, from the definition given, fixes it as a girder in distinction from a beam; and in speaking of such a case, one should say that the girder consists of an I beam. In ordering the material, however, the shape should be referred to as an I beam and not as an I girder.

Similarly, a channel may be used in a position which, from the definition, would fix it as a beam. In referring to it, one should say that the beam consists of a channel; and in ordering material, it should be referred to as a channel and not as a beam.

The beam may in some cases be made of sections riveted together, and, in such cases, would be referred to, in ordering, as a riveted girder. Frequentty, also, two beams bolted together are used, and are then called beam girders. It will be seen, therefore, that there are two distinct uses of these terms, beams and girders - the first depending on the manner of loading, and the second on the particular form of section of the member used. These two uses should never be confounded, as serious results might follow, especially in ordering material.

Uses of Sections. Each of the rolled sections has certain uses to which it is especially adapted, and for which it is most generally employed. I beams and channels are used principally as beams and girders to carry floors, roofs and walls. I beams are used to some extent also as columns, when the loads are relatively light. Channels are rarely used singly as columns; but they are used quite extensively in pairs latticed, and in combination with other shapes, to serve the purposes of columns. (For illustrations of such uses see Plate I, Page 7, showing column sections.)

Channels are also used to some extent in pairs latticed, or with plates across flanges, for the chords in trusses.

Angles are used most extensively in combination with other shapes to form columns, for members in trusses, and for the flanges of riveted girders. They are rarely used singly as columns except for light loads. As beams they are used only for very light loads, such as short lintels, ceilings, and roof purlins, when close spacing is necessary. They are used almost exclusively for the connections of beams and columns and of other members one with another, and for any position requiring a shelf for the support of other work.

The use of the angle is more varied than that of almost all other shapes, and it forms an essential part of nearly all riveted members.

Tees are rarely used in the construction of riveted members. Their principal uses are as beams of short spans and close spacing, where the loads are light and where a flange on each side of the center rib is necessary. Such instances occur in short lintels, ceil-ings, and certain cases of roofs, in skylights, pent houses and the like.

Zees are used extensively In columns, four zees being connected by a web plate or lattice bars also to some extent in lintels and light purlins. They are seldom used except where it is desirable to have the flanges arranged in this way, and usually angles or tees can be used to equal advantage with less expense.

Plates are used as connecting members in nearly all riveted work, but rarely alone except as bearing surfaces on masonry, and in some cases as shelves built in and projecting from masonary walls to receive other members.

Buckled Plates and Trough Plates are used almost exclus ively in bridge work for floors.

Corrugated Iron is used to a considerable extent in the siding and roofs of sheds and other buildings of a more or less temporary nature. Formerly it was used to some extent in fireproof floors as illustrated in "Fireproofing." This use, however, has almost entirely passed away.

Rods and Bars are used almost exclusively as tension members, for example, in trusses or as hangers.

Rules for Ordering. Material is never ordered simply from a schedule unless it is to be shipped plain, that is, merely cut to length without any shop work upon it. If there is to be any working of the material other than cutting to length, such as punching, riveting, or framing, a shop drawing is invariably necessary. Descriptions and uses of shop drawings will be given later.

If the material is simply to be cut to length, however, a schedule is sufficient; and in such cases the following rules should be observed:

1. Never give both the thickness and weight per foot of a piece. Beams and channels are invariably ordered by the depth and weight per foot, as a 12-inch I beam 31 1/2 lbs. per foot, or a 10-inch channel 15 lbs. per foot.

Angles are almost invariably ordered by giving the dimensions of legs and the thickness, as a 6 in. X 6 in. X 1/2 in. angle, or a 3 in. X 2 1/2 in. X 1/4 in. angle.

Zees are generally ordered by giving dimensions and thickness, as a 3 in. X 3 in. X 3/8in. Z, or a 4 in. X 3 in. X 5/16 in. Z. When unequal leg Z's are ordered, always give flange dimensions first.

In ordering tees, the dimensions and weight per foot are given, because the stem of a tee tapers. Thus a 3 in. X 3 in. 6.6-lb. T, or a 3 1/2 in. X 3 12 in. 9.2-lb. T. Here, as in the case of a Z, give flange dimensions first.

Plates are ordered by quoting width and thickness, as a 12 in. X 1/2 in. plate. The same applies to bars and flats.

Square and round rods are ordered by giving dimensions of the cross-section, as a 7/8-in. diameter rod, or a 2 in. X 2 in. rod.

2. All material, unless otherwise ordered, is subject to a standard variation in length of § inch. That is, it may be 3/8 inch over or under the specified length. If exact length is required, therefore, it is necessary to add after the specified length the word "exact."

3. If material is to be painted, the number of coats and kind of paint must be specified, as " Paint, one coat graphite."

4. Full shipping directions must be given, including the name of party or parties to whom order is to be billed, name of consignee, nearest railroad station, and route over which shipment is to be made.

5. Always avoid using special shapes and weights if time of delivery is any consideration, even at the expense of a little extra weight, unless special arrangement is made in advance as to the delivery which can surely be made It is more important to avoid the delay that would hinder progress in all branches of the work on a building through waiting for a few pieces of steel, than it is to save a few pounds by the use of special shapes and weights.