Ask the Expert: ASTM Strength Levels of A449 and A354 vs. SAE Strength Levels Grades 5 and 8

Ask the Expert: ASTM Strength Levels of A449 and A354 vs. SAE Strength Levels Grades 5 and 8

Question: What is the difference between hex head caps screws made to the ASTM strength levels of A449 and A354 grade BD as compared to the SAE strength levels grades 5 and 8?

Answer: In the U.S., the majority of hex bolts and hex cap screws, in diameters from 1/4” to 1 1/2”, are made and certified to the SAE grades 2, 5 and 8 (per SAE J429). The transportation/automotive market is the largest segment of the U.S. fastener industry and the grades that are manufactured for these markets are the most commonly available.

We regularly receive request for quotes from designers that work in the structural industry for ASTM grades of hex bolts and screws. When we receive these requests, we offer the SAE grade that corresponds to the ASTM grade. Conversely, we also receive RFQs from designer that are used to working with the SAE grades for larger diameter bolts that are not available in the SAE grades.

Below are the SAE grades that correspond to the most common ASTM strength levels: 

SAE Grades vs. ASTM Strength Levels

There are differences in the chemical composition of the material that can be used to make SAE certified bolts as compared to ASTM certified bolts. The ASTM specs tend to be tighter on the allowable carbon content than what SAE permits.

Most distributors of hex bolts and screws will stock the SAE grades in diameters up to 1 1/2” and the ASTM grades for diameters above 1 1/2”. This is because the SAE spec J429 only covers diameters from 1/4” to 1 1/2”. When we make hex cap screws in diameters larger than 1 1/2” we need a spec that covers these diameters that we can certify to so we use the ASTM specs.

At Earnest we stock grade 5 and 8 strength level bolts in diameters up to 1 1/2” and for sizes over 1 1/2” we stock A449 and A354 Gr BD. Below is a comparison on the head markings that these fasteners have. The certs for these grades will state the spec that they have been certified to base on the diameter of the product. 

Head Markings A449 and A 354 Gr BD