In all structural steel detailing certain abbreviations are so commonly used that it is essential at the outset for the student to be familiar with them. The more common are given below:




Steel Construction Definitions And Abbreviations 0500203











Round Rod, and when this mark follows a dimension, as for example, 3/4" o, it indicates a 3/4" diameter round rod.






O. H.


Open Hearth.

R. W.






R. & L.


Right and Left.






Hard Pine.

Y. P.


Yellow Pine.




U. H.


Under Head.

T. &G.


Tar & Gravel (also used for tongued and grooved). The right meaning can generally be inferred from the place in which the abbreviation occurs.



Rivet or Rivets.




Cor. I.


Corrugated Iron,












Floor Beam



Cast Iron.







W. G.


Wheel Guard.

c. to c.


Center to Center.

o. to o.


Out to out, or, outside to outside













The following definitions apply to pieces often met with in detailing and should be fully understood.

Lag Screws. These are used for connecting wooden construction, and their principal use, so far as the structural draftsman is interested, is for fastening guard rails to plank flooring on highway bridges, or to cross ties on railroad bridges, or wood purlins on roof trusses

Fitting=up Bolts. This term is applied to bolts used to con-nect parts of a member, or to connect members to each other, prior to riveting. The bolts are removed and rivets driven in their stead. In making out the shop lists where work is to be erected, a number of these bolts must be included, and about 10% more should be ordered than will appear to be necessary, in order to allow for waste. Fitting-up bolts are used in the shop during the assembling of the parts of any member of a structure.

Drift Pins. These are merely tapered steel pins used for aligning the rivet holes so that fitting up bolts may be inserted. Drift pins are also used in many cases to correct inaccuracies in the punching of the several parts of a member. If the holes do not match, so that the rivet can be driven through, the drift pin is first driven through and the edges of holes forced out so as to allow the rivet to be inserted. This is a use of drift pins which is not allowed by any first-class specifications, nevertheless it is often done, unless the shop work is rigidly inspected.

Pilot Nuts. A pilot nut is a tapered end which is temporarily screwed on to the end of a pin in order to effect a passage for it through the pin holes of two or more members which are to be connected in the field. These are, of course, only needed in pin connected structures, but must not be overlooked in making out shop orders and shipping lists, and at least one must be sent for each size of pin used in the structure.

Split Nuts. Owing to lack of room it is sometimes impossible to use a standard nut, and in such cases a thin split nut of about one-half the thickness of a standard nut may be used.

Plate Nuts. For the ends of large pins the nuts are sometimes made from plate cut to hexagon shape and tapped out to fit the threads on the ends of the pins.

Lomas Nuts. These are for use on the ends of large pins such as are used in bridge work. The pins are generally turned down to a smaller diameter at the ends, and these small ends threaded. A Lomas nut grips these threaded ends and projects over the shoulder of the pin. For dimensions and weights of Cambria standard pin nuts see Cambria Handbook, page 336.

Clevis Nuts. On page 334 of Cambria Handbook are shown sketches of clevis nuts, and table giving dimensions, etc., is given. As will be seen in the sketch, the screw ends entering the clevis nut allow the effective length of rod to be adjusted.

Sleeve Nuts. On page 333 of Cambria Handbook is found an illustration and table of dimensions, etc. The purpose of sleeve nuts, as will appear from the illustration, is to allow rods to be adjusted as to their length when the ends are connected to pins or bolts.

Turnbuckles. An illustration of an open turnbuckle is shown on page 332 of Cambria Handbook. Turnbuckles are used the same as sleeve nuts.

Tie Rods. Tie rods are plain rods with screw ends and nuts on each end, and they are used between the beams supporting fireproof floors to tie the beams together and to hold them in position while the fireproofing is being put in place. The tie rods also stiffen the I-beams laterally. The sizes of rods used for this purpose are usually 5/8-in. diameter to 1-in. diameter. See Fig. 207.

Loop Eye Rods. Rods which are connected to other parts of a structure by pins are provided with loops made by bending the rod around to conform to a circle of same diameter as the pin, and welding the end into the body of the rod. The distance from the center of pin to the junction of the end of loop with the main rod is usually made about two and a half times the diameter of the pin which loop is to connect over. See Fig. 188.

Forked Eye Rods. Sometimes it is desirable to have a rod connecting to a pin fastened so as to bring an equal strain on each side of another rod or part connecting to the same pin. In such cases it is necessary to make a forked eye instead of a single loop. See Fig. 188.

Upset Rods. When rods are threaded at the ends, the cutting of the threads diminishes the effective area of the rod and consequently weakens it. To maintain the same strength throughout, the rod is "upset" at the ends before the ends are threaded, and the amount of extra thickness so provided allows the threads to be cut, and leaves after cutting a net area equal to that in the body of the rod.

Upsetting is done by a machine which takes hold of the heated end of the rod when at a cherry-red heat and compresses the metal for the required length into a cylindrical end larger in diameter than the main body of the original rod. See pages 326 to 329 of Cambria Handbook.

Plain Rod. The expression "plain rod" is simply the negative of the term "upset rod", which has just been refined, or, in other words, a "plain rod" is not upset.

Standard Threads. Rods and bolts are generally provided with standard threads the dimensions of which will be found on page 316 of Cambria Handbook.

Right=hand Threads. When the threads of a bolt or rod are cut so that if, when looking at the end of the bolt or rod and turning the nut from left to right, the nut moves from you, or is screwed on the threads, then such threads are referred to as right-hand threads. If the threads are cut so that the reverse is true then they are "left-hand threads".