Fig. 27 shows three views of a square head or nut with chamfer corresponding to that on the hexagonal head in Fig. 23; and Fig. 28 shows the square head or nut chamfered to correspond to Fig. 26. Referring first to Fig. 27, the arc on the side view which shows the short diameter of the nut is drawn with a radius A, equal to two and one-quarter times the diameter of the bolt on which the head or nut belongs. The arcs on the other side view are drawn with a radius B, equal to one-half of A. The lines EF are drawn from points E tangent to the arcs, and it will be found that the points of tangency will come almost at the points where the arcs cut the single thread the notches on one side have their outer points opposite the inner points of the notches on the other side. For a double thread the notches are directly opposite each other lines CD. Points E are found by projecting from the plan view as indicated.

Fig. 27. Three Views of Square Head or Nut with Chamfer.

Fig. 28. Three Views of Square Head or Nut with Chamfer.

## Table III. Rough Square And Hexagon Bolt Heads. U. S. Standard

(franklin institute)

 Diameter of Bolt Width of Head Thickness of Head 1/4 1/2 3/4 5/16 19/32 19/34 3/8 11/16 11/22 7/16 25/22 75/64 1/2 7/8 7/16 9/16 21/22 31/64 5/8 1 1/16 17/32 3/4 1 1/4 5/8 7/8 1 7/16 23/32 ._
 Diameter [of Bolt| Width of Head Thickness of Head 1 1 5/8 13/16 1 1/8 1 13/16 29/32 1 1/4 2 1 1 3/8 2 3/16 1 3/22 1 1/2 2 3/8 1 3/16 1 5/8 2 9/16 1 9/22 1 3/4 2 3/4 1 3/8 1 7/8 2 15/169 1 15/32 2 3 1/8 1 9/16 2 1/4 3 1/2 1 3/4 2 1/2 3 7/8 1 13/16

## Table IV. Rough Square And Hexagon Nuts. U. S. Standard

(franklin institute).

 Diameter of Bolt Width of Nut Thickness of Nut 1/4 1/2 1/4 5/16 19/32 5/16 3/8 11/16 3/8 7/16 25/32 7/16 1/2 7/8 1/2 9/16 21/32 9/16 5/8 1 1/16 5/8 3/4 1 1/4 3/4 7/8 1 7/16 7/8
 Diameter ;of Bolt Width of Nut Thickness of Nut 1 1 5/8 1 1 1/8 1 13/16 1 1/8 1 1/4 2 1 1/4 1 3/8 2 3/16 1 3/8 1 1/2 2 3/8 1 1/2 1 5/8 2 9/16 1 5/8 1 3/4 2 3/4 1 3/4 1 7/2 2 15/14 1 7/8 2 3 1/8 2 2 1/4 3 1/2 2 1/4 2 1/2 3 7/8 2 1/2

In Fig. 28, the construction is similar. The points N are first found by projecting from the top and bottom of the circle in the plan view; then the lines NL are drawn, making angles of 30° with the line NN. (The proportions for the radii which are given, hold good only when the angle of 30° is used.) Next draw the construction line LL and draw the arc tangent to it with a radius A equal to two and one-quarter times the diameter of the bolt, the same as in Fig. 27. To draw the chamfer in the other side view, draw the construction line parallel to and at a distance from CC equal to the distance LL from NN and draw the arcs tangent to this line with radius B equal to one-half of A. The lines EF are then drawn as explained for Fig. 27.

Most of the bolts in common use are made standard sizes, that is, for a certain diameter of bolt there are a corresponding standard diameter and thickness for the head and the nut, and a standard number of threads per inch, so that if the bolt which the draftsman wishes to use has these standard dimensions they may be omitted from the drawing and a note made that the bolt is standard. Then the only dimensions necessary to be given are the diameter, the length under the head, and the length of the threaded part.

Tables III and IV give the United States standard sizes of square and hexagonal heads and nuts for bolts. The columns headed "Width of Nut" and "Width of Head" give the shortest dimension of the square or hexagon, that is, the diameter of the inscribed circle, or the distance across flats. The standard number of threads per inch can be found from the table already given.