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Sales Systems Limited Products and Services > Fasteners > Nuts > Structural Bolting [Nuts] > Heavy Hex Flat Nuts > Item # HHFN13750XXX  
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Item # HHFN13750XXX, Heavy Hex Flat Nut, 1-3/8" Nominal Dia.

  • Unification. Bold type indicates products unified dimensionally with British and Canadian standards.
  • Smaller Sizes. For sizes 1/4 in. through 1 in., the nuts specified in Table are recommended.
  • Tops of Nuts. Tops of nuts shall be flat and chamfered. Diameter of the chamfer circle shall be equal to the maximum width across flats within a tolerance of minus 15 percent. The length of chamfer at hex corners shall be from 5 to 15 percent of the basic thread diameter. The surface of chamfer may be slightly convex or rounded.
  • Width Across Flats. Maximum width across flats shall not be exceeded. No transverse section through the nut between 25 and 75 percent of the actual nut thickness as measured from the bearing surface shall be less than the minimum width across flats. For milled-from-bar nuts, see statement in General Data pertaining to the nominal bar size to be used.
  • Corner Fill. A rounding or lack of fill at junction of hex corners with chamfer shall be permissible provided the width across corners is within specified limits at and beyond a distance equal to 17.5 percent of the basic thread diameter from the chamfered face.
  • Bearing Surface. Bearing surface shall be flat and perpendicular to the axis of the threaded hole within a tolerance of 2 deg.
  • True Position of Tapped Hole. The axis of tapped hole shall be located at true position with respect to the axis of nut body within a tolerance zone having a diameter equivalent to 4 percent of the maximum width across flats for 1-1/2 in. nominal size nuts or smaller, and 6 percent of the maximum width across flats for nuts larger than 1-1/2 in., regardless of feature size.
  • Threads. Threads shall be Unified coarse thread series (UNC series), Class 2B, in accordance with ASME B1 .1.
  • Material. Unless otherwise specified, chemical and mechanical properties of steel nuts shall conform with Grade A of ASTM A563. Nuts of other materials such as corrosion resistant (stainless) steel, brass, bronze and aluminum alloys shall have properties as agreed upon between the manufacturer and purchaser. The properties for nuts of several grades of corrosion resistant steel alloys are covered in ASTM F594, and of several nonferrous materials in ASTM F467.
  • Nominal Size. Where specifying nominal size in decimals, zeros preceding the decimal and in the fourth decimal place shall be omitted.

Manufacturer  · Specifications  · Codes and Standards



Industrial Fasteners Institute




Unit of Measure


Nominal Size or Basic Major Dia. of Thread

1-3/8 in

Nominal Size or Basic Major Dia. of Thread (Decimal)

1.3750 in

Basic Width Across Flats (F)

2-3/16 in

Max. Width Across Flats (F)

2.188 in

Min. Width Across Flats (F)

2.119 in

Max. Width Across Corners (G)

2.526 in

Min. Width Across Corners (G)

2.416 in

Basic Thickness (H)

1-3/8 in

Max. Thickness (H)

1.409 in

Min. Thickness (H)

1.310 in

Codes and Standards

Codes and Standards

ASME/ANSI B18.2.2 1987 (R 1999)


Formulas for Nut Dimensions
(PDF, 296KB)

Wrench Openings for Square and Hex Nuts
(PDF, 244KB)

Distributor of Industry Standard and Military Specification Threaded Fasteners