| 3-7/16
4-3/4 |4.256 | 2-5/8 | 8-3/8 |10-1/4 | 7-1/4 | 4-3/4 | 3-5/8
5 |4.480 | 2-1/2 | 8-13/16|10-25/32| 7-5/8 | 5 | 3-13/16
5-1/4 |4.730 | 2-1/2 | 9-1/4 |11-5/16 | 8 | 5-1/4 | 4
5-1/2 |4.953 | 2-3/8 | 9-11/16|11-27/32| 8-3/8 | 5-1/2 | 4-3/16
5-3/4 |5.203 | 2-3/8 |10-3/32 |12-3/8 | 8-3/4 | 5-3/4 | 4-3/8
6 |5.423 | 2-1/4 |10-17/32|12-29/32| 9-1/8 | 6 | 4-9/16
-------+------+---------+--------+--------+----------+----------+----------
* Diameter at the root of the thread.

The basis of the Franklin Institute or United States standard for the
heads of bolts and for nuts is as follows:

The short diameter or width across the flats is equal to one and
one-half times the diameter plus 1/8 inch for rough or unfinished bolts
and nuts, and one and one-half times the bolt diameter plus, 1/16 inch
for finished heads and nuts. The thickness is, for rough heads and nuts,
equal to the diameter of the bolt, and for finished heads and nuts 1/16
inch less.

[Illustration: Fig. 155.]

[Illustration: Fig. 156.]

The hexagonal or hexagon (as they are termed in the shop) heads of bolts
may be presented in two ways, as is shown in Figures 155 and 156.

The latter is preferable, inasmuch as it shows the width across the
flats, which is the dimension that is worked to, because it is where the
wrench fits, and therefore of most importance; whereas the latter gives
the length of a flat, which is not worked to, except incidentally, as it
were. There is the objection to the view of the head, given in Figure
156, however, that unless it is accompanied by an end view it somewhat
resembles a similar view of a square head for a bolt. It may be
distinguished therefrom, however, in the following points:

If the amount of chamfer is such as to leave the chamfer circle (as
circle A, in Figure 153) of smaller diameter than the width across the
flats of the bolt-head, the outline of the sides of the head will pass
above the arcs at the top of the flats, and there will be two small flat
places, as A and B, in Figure 156 (representing the angle of the
chamfer), which will not meet the arcs at the top of the flats, but will
join the sides above those arcs, as in the figure; which is also the
case in a similar view of a square-headed bolt. It may be distinguished
therefrom, however, in the following points:

If the amount of chamfer is such as to leave the chamfer circle