Why this title? Do steel structure bolts have grades? Can they be classified into 4.8, 8.8, or other strength grades like other bolts? In hardware sales, we sometimes encounter customers purchasing large hex head bolts. It should be clarified that in national standards, large hex head bolts are not equivalent to steel structure bolts-large hex head bolts in the category of steel structure bolts are products with specific standards, while ordinary large hex head bolts may have different strength grades. In national standards, steel structure bolts correspond to only one strength grade: 10.9. If a customer needs 8.8-grade large hex head bolts, such bolts actually belong to ordinary high-strength bolts, not steel structure bolts as defined by national standards. This raises a question: are there steel structure bolts of other grades?
To be clear, in national standards, steel structure bolts correspond to only one strength grade: 10.9, with no other strength specifications. If customers have other strength requirements, these are special needs in practical applications, not aligned with national standards, but this does not affect the production and use of bolts-after all, standards are formulated based on practical applications. We raise this question to help users better understand the performance and related knowledge of steel structure bolts, avoiding mistakes in procurement. Unless special requirements are involved, steel structure bolts available on the market should be the standard 10.9-grade. Only by clarifying the standards can buyers avoid being misled by unscrupulous merchants.
If we really need to classify steel structure bolts, it can only be based on their appearance standards. Among steel structure bolts, there is another type called twist-off type steel structure bolts. Their heads are not designed with large hexagon across flats but are similar to mushroom heads, which can be easily distinguished by appearance, and their installation methods are slightly different. However, such twist-off type steel structure bolts are less commonly used, so this article still focuses on the more common large hex head steel structure bolts.
Compared with ordinary bolts, steel structure bolts differ in specifications. Ordinary bolts can be as small as M3, and some are even smaller, while the minimum specification of steel structure bolts is M16, with the shortest length being 50mm, so they are classified as medium to large bolts. This is mainly because steel structure bolts are mostly used in building construction and bridge installation, which have high requirements for load-bearing performance. If the size is too small, theoretically, they cannot meet the needs of the application environment.
Ordinary bolts are usually supplied individually, meaning you get only a bolt if you order one, and nuts need to be purchased separately. In contrast, steel structure bolts are supplied as a set with washers and nuts. Their washers are high-strength products, hardened by heat treatment, and their nuts are designed with large hexagon across flats, thickened and widened, with a strength grade of 10.
