ASME B18.2.6 – Dimensions Charts

ASME B18.2.6 is the American National Standard for Fasteners for Use in Structural Applications. This standard provides complete general and dimensional data for five key structural products: heavy hex structural bolts, heavy hex nuts, hardened steel washers, compressible washer-type direct tension indicators, and twist-off-type tension control structural bolts. Use the dimension charts below to find full specifications—including head dimensions, body diameters, thread lengths, and tolerances—for high-strength fasteners conforming to ASTM A325, A490, A563, F436, F959, and F1852.

Dimensions & Size Chart

Heavy Hex Bolt For Structural Application Dimensions
Bolt Size		1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
E	Min	0.482	0.605	0.729	0.852	0.976	1.098	1.223	1.345	1.47
E	Max	0.515	0.642	0.768	0.895	1.022	1.149	1.277	1.404	1.531
F	Min	0.85	1.031	1.212	1.394	1.575	1.756	1.938	2.119	2.3
F	Max	0.875	1.062	1.25	1.438	1.625	1.812	2	2.188	2.375
G	Min	0.969	1.175	1.383	1.589	1.796	2.002	2.209	2.416	2.622
G	Max	1.01	1.227	1.443	1.66	1.876	2.093	2.309	2.526	2.742
H	Min	0.302	0.378	0.455	0.531	0.591	0.658	0.749	0.81	0.902
H	Max	0.323	0.403	0.483	0.563	0.627	0.718	0.813	0.878	0.974
R	Min	0.009	0.021	0.021	0.031	0.062	0.062	0.062	0.062	0.062
R	Max	0.031	0.062	0.062	0.062	0.093	0.093	0.093	0.093	0.093
Y	Reference	0.19	0.22	0.25	0.28	0.31	0.34	0.38	0.44	0.44
LT	Reference	1	1.25	1.38	1.5	1.75	2	2	2.25	2.25

Note: All measurements are in inches

Disclaimer: The dimensions presented on this page are based on the applicable industry standard. However, actual product measurements may vary slightly due to manufacturing practices, material selection, surface finish, and specified tolerance classes. Buyers and sourcing professionals are encouraged to verify final specifications with the manufacturer or supplier prior to procurement, particularly for critical applications.

Legend

E – Body Diameter: The thickness of the unthreaded shank used to calculate the necessary clearance hole size and determine the bolt’s overall shear strength.
F – Width Across Flats: The distance between two parallel flat surfaces of the bolt head, used to identify the correct wrench or spanner size for installation.
G – Width Across Corners: The maximum diameter of the hexagonal head measured from point to point, ensuring enough clearance for the tool to rotate.
H – Head Height: The vertical thickness of the head, critical for ensuring the bolt does not protrude or interfere with moving components in tight assemblies.
R – Radius of Underhead Fillet: The curved transition where the shank meets the head; it provides essential stress relief to prevent the head from snapping under tension.
LT – Thread Length: The portion of the bolt featuring functional threads, determining the maximum engagement depth into a tapped hole or nut.
L – Nominal Length: The total reach of the fastener from the under-head bearing surface to the tip.
L_G – Grip Length: The distance from the head to the first full thread (the unthreaded shear plane).

Technical Note

Maximum Grip Gaging Length (L_G, max)
- Definition: The distance parallel to the bolt axis from the underhead bearing surface to the face of a noncounterbored or noncountersunk standard GO thread ring gage, assembled by hand as far as the thread will permit.
- Calculation (Not Full Length): L_G max = L_nom - L_T (rounded to two decimal places).
- Calculation (Full Length): Defines the unthreaded length under the head. Shall not exceed 2.5 times the thread pitch (P) for sizes ≤ 1 in., and 3.5 times the pitch for sizes > 1 in.
Minimum Body Length (L_B, min)
- Definition: The distance parallel to the bolt axis from the underhead bearing surface to the last scratch of thread, or to the top of the extrusion angle.
- Calculation: L_B min = L_G max - Y (where Y is the transition thread length, rounded to two decimal places).
L_G & L_B Calculation Example
- Bolt Size : 7/16-14 x 4.000 in.
- Pitch (P) : 1 ÷ 14 TPI = 0.0714 in
- L_G (Max) : 4.000 - 1.380 = 2.620 in
- L_B (Min) : 2.620 - Y (Transition thread length from Table 2)
- Minimum Design Grip Length : 2.620 - (5 x 0.0714) = 2.263 in
  (Reflects the tolerance of minus five coarse thread pitches)
Length - Standard increments and permissible tolerances based on nominal bolt size and length:
- For nominal bolt sizes 1/4 to 1.00 in.:
  - Up to 1.00 in. lengths: 0.06 to 0.13 in. increments with a tolerance of +0.02 / -0.03.
  - Over 1.00 through 2.50 in. lengths: 0.25 in. increments with tolerances ranging from +0.02 / -0.04 for smaller diameters to +0.08 / -0.10 for 1.00 in. bolts.
  - Over 2.50 through 4.00 in. lengths: 0.25 in. increments with tolerances ranging from +0.04 / -0.06 to +0.10 / -0.14.
  - Over 4.00 through 6.00 in. lengths: 0.50 in. increments with tolerances ranging from +0.06 / -0.10 to +0.12 / -0.16.
  - Longer than 6.00 in. lengths: 1.00 in. increments with tolerances ranging from +0.10 / -0.18 to +0.16 / -0.20.
- For nominal bolt sizes over 1.00 in.:
  - Over 1.00 through 2.50 in. lengths: 0.50 in. increments with tolerances ranging from +0.12 / -0.12 to +0.18 / -0.18.
  - Over 2.50 through 4.00 in. lengths: 0.50 in. increments with tolerances ranging from +0.16 / -0.16 to +0.20 / -0.20.
  - Over 4.00 through 6.00 in. lengths: 0.50 in. increments with tolerances ranging from +0.18 / -0.18 to +0.22 / -0.22.
  - Longer than 6.00 in. lengths: 1.00 to 2.00 in. increments with tolerances ranging from +0.22 / -0.22 to +0.24 / -0.24.

Heavy Hex Nut For Structural Application Dimensions
Nut Size		1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
F	Min	0.85	1.031	1.212	1.394	1.575	1.756	1.938	2.119	2.3
F	Max	0.875	1.062	1.25	1.438	1.625	1.812	2	2.188	2.375
G	Min	0.969	1.175	1.382	1.589	1.796	2.002	2.209	2.416	2.622
G	Max	1.01	1.227	1.443	1.66	1.876	2.093	2.309	2.526	2.742
H	Min	0.464	0.587	0.71	0.833	0.956	1.079	1.187	1.31	1.433
H	Max	0.504	0.631	0.758	0.885	1.012	1.139	1.215	1.378	1.505

Note: All measurements are in inches

Legend

F – Width Across Flats: The distance between two parallel flat surfaces of the nut, used to identify the correct wrench or socket size for installation.
G – Width Across Corners: The maximum diameter of the nut measured from point to point, ensuring enough clearance for the tool to rotate within an assembly.
H – Hex Nut Thickness / Height: The total vertical thickness of a standard hex nut, providing the necessary thread engagement to meet its proof load rating.

Hardened Washer For Structural Application Dimensions
Washer Size		1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
A	Nominal	0.531	0.688	0.813	0.938	1.125	1.25	1.375	1.5	1.625
	Min	0.531	0.688	0.813	0.938	1.125	1.25	1.375	1.5	1.625
	Max	0.5623	0.7193	0.8443	0.9693	1.1563	1.2813	1.4063	1.5313	1.6563
B	Nominal	1.063	1.313	1.469	1.75	2	2.25	2.5	2.75	3
	Min	1.0317	1.2817	1.4377	1.7187	1.9687	2.2187	2.4687	2.7187	2.9687
	Max	1.0943	1.3443	1.5003	1.7813	2.0313	2.2813	2.5313	2.7813	3.0313
C	Min	0.097	0.122	0.122	0.136	0.136	0.136	0.136	0.136	0.136
C	Max	0.177	0.177	0.177	0.177	0.177	0.177	0.177	0.177	0.177
E	Nominal	0.438	0.547	0.656	0.766	0.875	0.984	1.094	1.023	1.313

Note: All measurements are in inches

Legend

A – Inside Diameter: The inner clearance hole dimension, designed to fit over the bolt shank while providing adequate bearing surface under the head or nut.
B – Outside Diameter: The total width of the washer, which distributes the clamping load over a specific area of the connected material.
C – Thickness: The vertical height of the washer, critical for maintaining structural rigidity and meeting ASTM specifications for hardened fasteners.
E – Nominal Edge Distance: Specific to clipped washers, this is the distance from the center of the washer to the flat (clipped) edge, used where clearance is limited by an adjacent structural member.

Hardened Beveled Washer For Structural Application Dimensions
Washer Size		1/2	5/8	3/4	7/8	1	1-1/8	1-1/4	1-3/8	1-1/2
A	Nominal	0.531	0.688	0.813	0.938	1.125	1.25	1.375	1.5	1.625
	Min	0.531	0.688	0.813	0.938	1.125	1.25	1.375	1.5	1.625
	Max	0.5623	0.7193	0.8443	0.9693	1.1563	1.2813	1.4063	1.5313	1.6563
L	Min	1.75	1.75	1.75	1.75	1.75	2.25	2.25	2.25	2.25
T	Nominal	0.313	0.313	0.313	0.313	0.313	0.313	0.313	0.313	0.313
E	Nominal	0.483	0.547	0.656	0.766	0.875	0.984	1.094	1.203	1.313

Note: All measurements are in inches

Legend

A – Inside Diameter: The inner hole dimension designed to accommodate the bolt shank while maintaining a proper bearing surface on sloped structural flanges.
L – Side Length: The overall width of the square washer body, providing the necessary surface area to bridge structural gaps and distribute the clamping load.
T – Thickness: The mean or average vertical height of the washer, ensuring it meets the specific hardening and strength requirements for structural assemblies.
E – Nominal Edge Distance: The distance from the center of the bolt hole to the edge of the washer, critical for ensuring the washer does not interfere with the web of a channel or I-beam.

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ASME B18.2.6 – Dimensions Charts

Dimensions & Size Chart

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