Stainless Steel Double-Ended Bolts

There are various standards for stainless steel double-ended bolts, such as GB/T 901A and GB/T 901B. A double-ended bolt has threads at both ends and a smooth shank in the middle, which is how it gets its name. The suffix letters "A" and "B" in the standards have different meanings: Type A indicates a thick shank specification, while Type B indicates a thin shank specification. The dimensions for the thick and thin shanks follow clear standards and are not arbitrarily set.

For the thick shank, the diameter of the smooth shank is consistent with the major diameter of the thread. For example, a thick-shank double-ended bolt with an M16 thread has a smooth shank diameter of 16 mm (with a certain negative tolerance range). For the thin shank, the diameter of the smooth shank corresponds to the wire diameter before thread rolling (close to the pitch diameter of the thread). For example, if the wire diameter of an M16 thread before rolling is approximately 14.2 mm, the diameter of the thin smooth shank is exactly this size.

Stainless steel double-ended bolts are widely used for connecting valves and flanges, and their installation is convenient: after passing through the reserved hole, tighten nuts at both ends. It is necessary to note the tendency of stainless steel materials to seize (gall) during installation; anti-seize compound can be used to prevent this. With the development of industry, many large-scale equipment (such as pressure vessels and mining machinery) have adopted stainless steel double-ended bolts.

A variety of materials can be used to produce double-ended bolts. In addition to 304 and 316 stainless steel, various grades of carbon steel, medium carbon steel, and high-strength alloy steel are also applicable. It should be noted that our company currently cannot provide a special material-A193-B7 (American standard high-temperature and high-strength alloy material), which is mainly used in the pressure vessel industry. Although some materials can be used as temporary substitutes, pressure vessels are special equipment, and accidents can lead to serious consequences. Therefore, arbitrary substitution is not recommended.

We remind users: A193-B7 material was originally imported, and many domestic users directly replace it with 42CrMoA. Although their performance is similar and there is no obvious problem in ordinary environments, 42CrMoA is not the material specified in the design, so caution is required when used in special equipment.

The production process of stainless steel double-ended bolts is relatively simple: wire rod is used as the raw material, which is cut and then subjected to thread rolling at both ends. Thick-shank specifications do not require additional turning (only wire rods matching the major thread diameter need to be selected), while thin-shank specifications directly use wire rods with the diameter before thread rolling. The low production entry threshold (simple equipment is sufficient for production) allows most enterprises to manufacture double-ended bolts.

Double-ended bolts are the most commonly used fasteners in the list of reducer components. Since reducers operate at high speed for a long time, the wear of double-ended bolts is severe. It is necessary to regularly inspect the thread tightness of the bolts and replace the matching nuts periodically (it is recommended to use two nuts for each end of the thread). If the thread of the double-ended bolt is damaged, do not only replace the nut- the entire double-ended bolt must be replaced with a new one.

The purpose and standards of conventional double-ended bolts are intuitively understandable, and acceptance inspection is convenient. This article focuses on an unconventional double-ended bolt-the unequal-length stud bolt of GB/T 897 standard. Its special features are as follows (explained with technical drawings):

The left one is an M8×50 stainless steel double-ended bolt, the middle is an M10×60 standard, and the right one is an M10×90 stainless steel double-ended bolt. Have you noticed the difference? That's right-it's the specification for length measurement. For commonly used double-ended bolts, we measure their total length. However, the length marked for the unequal-length double-ended bolts in the above drawings does not include the thread length of one end (usually the shorter end). Moreover, the thread length of this standard has a fixed corresponding relationship with the thread diameter; mastering this key point allows for accurate identification.

In another set of drawings, the left one is an M12×70, the middle is an M16×90, and the right one is an M20×150 stainless steel double-ended bolt. The above are common specifications of unequal-length double-ended bolts. The thread diameter is fixed, and the length can be customized and purchased according to actual needs.