Bolt grade indicates the mechanical performance requirements of a fastener and is an important consideration when selecting bolts for an application. For buyers working with an industrial fastener manufacturer, understanding bolt grades and the standards behind them can help ensure the selected fastener meets the required specifications. Common designations include 8.8, 10.9, and 12.9 under ISO 898-1, as well as Grade 5 and Grade 8 under SAE J429.
Different applications use different bolt and fastener standards. Common standards include:
◆ Note: This table is provided for general reference only. Specific product requirements should be determined according to the applicable standard, technical documentation, and actual service conditions. Grades from different standards should not be treated as directly equivalent based only on their names or a single mechanical property.
It is also important to distinguish between a standard and a grade. For example, ISO 898-1 is a standard, while 8.8, 10.9, and 12.9 are property classes within that standard. Similarly, SAE J429 is a standard that uses classifications such as Grade 5 and Grade 8.
ISO 898-1 specifies mechanical and physical property requirements for carbon steel and alloy steel bolts, screws, and studs.
Among its property classes, 8.8, 10.9, and 12.9 are common designations. For example:
8.8
nominal tensile strength of 800 MPa
10.9
nominal tensile strength of 1,000 MPa
12.9
nominal tensile strength of 1,200 MPa
These figures are nominal values used in the property class designation. They should not be interpreted as the minimum tensile strength of every bolt in that class. Actual mechanical properties depend on the applicable size range and testing requirements specified by the standard.
SAE J429 specifies mechanical and material requirements for steel externally threaded fasteners and uses classifications such as Grade 2, Grade 5, and Grade 8.
These requirements are particularly relevant when specifying industrial bolts for a particular application, where grade, thread system, dimensions, and material all need to be considered.
Unlike ISO 898-1, which uses property classes such as 8.8 and 10.9, SAE J429 uses the term Grade. Therefore, an SAE Grade and an ISO Property Class should not automatically be treated as equivalent simply because their numbers appear similar.
When selecting a grade, also consider thread specifications, dimensions, material, heat treatment, and the actual load requirements of the application.
Although both ASTM A307 and ASTM F3125/F3125M cover steel bolts, they have different product scopes and performance requirements.
■ ASTM A307 — primarily covers general-purpose carbon steel bolts, studs, and threaded rods.
■ ASTM F3125/F3125M — covers high-strength structural bolts and related assemblies.
Therefore, two bolts should not be considered interchangeable simply because both are made of steel. The appropriate standard should be selected according to the design requirements and intended application.
▸ Different bolt grades cannot be simply converted on a one-to-one basis.
Standards may differ in grade definitions, mechanical property requirements, dimensional ranges, and intended applications. Even when certain performance values appear similar, one value alone is not enough to establish equivalence.
When replacing or purchasing bolts, confirm the standard, grade, thread system, dimensions, material, and service conditions rather than comparing only the Grade or Property Class number.
When selecting a bolt grade, consider the following factors:
Determine whether the bolt will be used for general fastening, machinery, structural connections, or another application.
Select a suitable property class or grade based on the design loads and connection requirements.
Check whether the drawings, specifications, or customer requirements call for ISO, SAE, ASTM, or another standard.
Confirm whether the fastener uses a metric or inch thread system, along with the required diameter, pitch, length, and thread type.
Consider the material, heat treatment, and surface treatment required for the working environment.
Bolt grades classify the mechanical performance requirements of fasteners. 8.8, 10.9, 12.9, Grade 5, and Grade 8 belong to different standard systems and should not be directly converted based only on their numbers.
For engineers and purchasing teams, selecting the right bolt requires consideration of the standard, grade, dimensions, material, and actual service conditions to determine whether a fastener is suitable for the application.
