Grade 1 & Grade 2 Hex Bolts
SAE J429 Grade 1 and Grade 2 bolt specifications cover 1/4- to 1 1/2-inch body diameter, low to medium carbon steel bolts. Their mechanical and strength properties, measured in pounds per square inch, and are found in the fastener mechanical properties for steel charts which can be viewed online or from the SAE handbook.
Grade 1 and Grade 2 bolts have no head marking. They are equivalent in strength and mechanical properties to the American Society of Testing Materials A307 specification for Grades A & B bolts.
Grade 1 and 2 bolts have the least strength and heat resistance properties of all the bolts within the SAE J429 specification.
Grade 5 Hex Bolts
SAE J429 Grade 5 bolt specifications cover bolts with 1/4- to 1 1/2-inch body diameter and made from medium carbon steel, quenched and tempered. Quenching and tempering are processes related to the heat treating of bolts for specific ductility and hardness values.
Grade 5 bolts are stronger and have more heat tolerance than Grade 1 and 2 bolts. Proof load, tensile and yield strength values are found on the fastener mechanical properties for steel charts.
Grade 5 bolts are marked by three equidistant lines beginning at the outer rim of the bolt's head to its center. Used for medium to heavy duty fastenings, Grade 5 bolts are equivalent to ASTM A449 bolts up to 1 1/2 inch body diameter.
Grade 5.2 Hex Bolts
SAE J429 Grade 52 bolts are marked by three equidistant lines beginning on the outer rim of the bolt head and meeting at its halfway point. Body diameter specifications are 1/4 to 1 inch.
Grade 52 bolts are made from low carbon martensitic steel, quenched and tempered. They are not as durable and heat resistant as Grade 5 bolts because they are made from soft and ductile low carbon martensitic steel.
Therefore, do not use Grade 52 bolts for an application that requires a Grade 5.
Grade 7 & 8 Hex Bolts
SAE J429 Grade 7 and 8 bolts are made from medium carbon high strength alloy steel, quenched and tempered. Used for automotive, structural and high temperature applications; they are the strongest and most heat resistant of all SAE graded bolts.
Their mechanical and strength properties are found on the fastener mechanical properties for steel charts on fastener distributor and manufacturer's websites or in the SAE and IFI handbooks. Grade 7 and 8 bolts are marked with five and six equidistant lines, respectively, beginning from the rim of the bolt head to its center.
Grade 8 bolts are equivalent to ASTM A354 Grade BD bolts.
Metric, Material, Hardness, Heat Treating
Besides US bolt standards, the SAE has standard J1199 for metric externally threaded fasteners. Metric bolt heads are marked with identifying numbers instead of lines.
For example, a metric bolt with an 88 head marking is equivalent to a Grade 5, and a 109 marked metric bolt is equivalent to a Grade 8. Bolt hardness, material and heat treating standards and specifications can be found in the "Related Standards" section in the SAE Fastener Standards Manual.