ASME B18.2.1 Hex Bolts | ASTM A193 Grade B7

zhao77jie — Wed, 04 Feb 2026 08:27:20 +0000

ASME B18.2.1 hex bolts are essential heavy-duty industrial fasteners. When hex bolts applied in ASTM A193 B7 material makes it stand out as a high-performance option for critical applications. This article details their core relevant standards, material composition and key industrial applications.

ASME B18.2.1 Standard

ASME B18.2.1 standard is globally recognized for establishing definitive dimensional, threading, and manufacturing tolerances for carbon and alloy steel bolts. It sets specifications for critical physical and mechanical design criteria for headed fasteners, including head geometry, shank measurements, thread pitch and fit, and length tolerances.

Also it ensures interchangeability and consistent performance across industrial fastening assemblies. This standard applies to the most commonly used industrial headed bolts and screws such as hex bolts, square head bolts, heavy hex bolts and so on. In this article, we mainly pay attention to ASME B18.2.1 hex bolts.

ASME B18.2.1 Hex Bolts

Hex bolts are one of the main bolts types under ASME B18.2.1 standard, with the hexagonal head as their most distinctive feature. Fully compliant with the standard ASME B18.2.1, hex bolts boast precise structural and dimensional characteristics. They contain a cylindrical shank (smooth or threaded), consistent thread pitch, and strict tolerance controls for head size and thickness.

Besides, hex bolts are available in both full-thread and partial-thread configurations, full-thread variants provide uniform load distribution along the entire bolt length, while partial-thread options offer enhanced rigidity in the unthreaded shank area for heavy load-bearing scenarios.

Hex Bolts Dimensions

Nominal Size or Basic Product Diameter		E		F			G		H			R		Lr
		Full-Size Body Diameter		Width Across Flats			Width Across Corners		Head Height			Radius of Fillet		Nominal Thread Length for Bolt Lengths
		Full-Size Body Diameter		Width Across Flats			Width Across Corners		Head Height			Radius of Fillet
		Max	Min	Basic	Max	Min	Max	Min	Basic	Max	Min	Max	Min	≤6 in	>6 in
1/4	0.2500	0.260	0.237	7/16	0.438	0.425	0.505	0.484	1/16	0.188	0.150	0.030	0.010	0.750	1.000
5/16	0.3125	0.324	0.298	1/2	0.500	0.484	0.577	0.552	7/32	0.235	0.195	0.030	0.010	0.875	1.125
3/8	0.3750	0.388	0.360	9/16	0.562	0.544	0.650	0.620	1/4	0.268	0.226	0.030	0.010	1.000	1.250
7/16	0.4375	0.452	0.421	5/8	0.625	0.603	0.722	0.687	19/64	0.316	0.272	0.030	0.010	1.125	1.375
1/2	0.5000	0.515	0.482	3/4	0.750	0.725	0.866	0.826	11/32	0.364	0.302	0.030	0.010	1.250	1.500
5/8	0.6250	0.642	0.605	15/16	0.938	0.906	1.083	1.033	27/64	0.444	0.378	0.060	0.020	1.500	1.750
3/4	0.7500	0.768	0.729	1-1/8	1.125	1.088	1.299	1.240	1/2	0.524	0.455	0.060	0.020	1.750	2.000
7/8	0.8750	0.895	0.852	1-5/16	1.312	1.269	1.516	1.447	37/64	0.604	0.531	0.060	0.020	2.000	2.250
1	1.0000	1.022	0.976	1-1/2	1.500	1.450	1.732	1.653	43/64	0.700	0.591	0.090	0.030	2.250	2.500
1-1/18	1.1250	1.149	1.098	1-11/16	1.688	1.631	1.949	1.859	3/4	0.780	0.658	0.090	0.030	2.500	2.750
1-1/4	1.2500	1.277	1.223	1-7/8	1.875	1.812	2.165	2.066	27/32	0.876	0.749	0.090	0.030	2.750	3.000
1-3/8	1.3750	1.404	1.345	2-1/16	2.062	1.994	2.382	2.273	29/32	0.940	0.810	0.09	0.03	3.000	3.250
1-1/2	1.5000	1.531	1.470	2-1/4	2.250	2.175	2.598	2.480	1	1.036	0.902	0.090	0.030	3.250	3.500
1-3/4	1.7500	1.785	1.716	2-5/8	2.625	2.538	3.031	2.893	1-5/32	1.196	1.054	0.120	0.040	3.750	4.000
2	2.0000	2.039	1.964	3	3.000	2.900	3.464	3.306	1-11/32	1.388	1.175	0.120	0.040	4.250	4.500

Introduction of ASTM A193 Standard

ASTM A193 is a critical material standard for alloy and stainless steel bolts (like hex bolts etc), specifically formulated for high-temperature, high-pressure, and critical service applications. This standard also defines the material requirements, heat treatment processes, and mechanical performance criteria for bolts used in oil and gas, petrochemical, and power generation industries.

ASTM A193 Grade B7 Chemical Composition

Element	Content Range
Carbon (C)	0.38 – 0.48
Manganese (Mn)	0.75 – 1.00
Phosphorus (P)	≤ 0.035
Sulfur (S)	≤ 0.040
Silicon (Si)	0.15 – 0.35
Chromium (Cr)	0.80 – 1.10
Molybdenum (Mo)	0.15 – 0.25

ASTM A193 Grade B7 Mechanical Property

Mechanical Requirements	Content Range
Tensile Strength	≤2in 125 ksi min 2–4in 115 ksi min 4–7in 100 ksi min
Yield Strength (0.2% offset)	≤2in 105 ksi min 2–4in 95 ksi min 4–7in 75 ksi min
Elongation in 4D %	≤4in 16 min 4–7in 18 min
Reduction of Area %	50 min
Hardness	321 HBW max Or 35 HRC max

ASTM A193 B7 Hex Bolts

ASTM A193 B7 hex bolts perfectly combine ASME B18.2.1 standard with the superior material performance of ASTM A193 Grade B7. Forged from high-strength chromium-molybdenum alloy steel and precision heat-treated, these bolts adhere to ASME B18.2.1’s standards for head geometry and tolerances, while meeting ASTM A193 Grade B7’s rigorous mechanical and material requirements. This dual compliance delivers the dimensional interchangeability of ASME B18.2.1 and the exceptional high-temperature resistance, tensile strength and load-bearing capacity of ASTM A193 B7, forming a high-performance fastener ideal for critical industrial fastening applications.

Applications

ASME B18.2.1 hex bolts per ASTM A193 Grade B7 are widely used in critical industrial sectors, including:

oil and gas piping systems

petrochemical pressure vessels

power generation turbines

heavy machinery etc.

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