The following are the usual proportions of square nuts and bolt-heads: - The width across the flats of black nuts may be one and a half times the diameter of the bolt, plus from .18 in. to .44 in.; or of bright nuts, one and a half times the diameter, plus from .06in. to .18 in. Across the angles, rough nuts may measure 2.12 times the diameter, plus from .25in. to .6 in.; and bright nuts, 212 times the diameter, plus from .08 in. to .25 in. The height of the bolt-head may be from two-thirds of the diameter of the bolt to equal to this diameter.