What Are Close Tolerance Bolts?

Close tolerance bolts by Monroe

Close tolerance bolts are commonly used in the aerospace manufacturing industry. They are threaded fasteners that feature a shank and head. The shank is threaded, thus allowing them to be driven into a threaded hole. Close tolerance bolts, however, are designed with a greater emphasis on measurement accuracy than other types of bolts. What are close tolerance bolts exactly, and how do they differ from traditional bolts?

The Basics of Close Tolerance Bolts

Close tolerance bolts are threaded fasteners with a tolerance of just +0.000, -0.0005 inch. This is the acceptable range of variance. Close tolerance bolts allow for almost no variance from their specified size. You can find them in different materials and styles, but they all have a tolerance of just +0.000, -0.0005 inc

Close Tolerance Bolts vs Traditional Bolts

Traditional bolts have a greater acceptable range of variance. Some o them may have a slightly larger shank than specified, whereas others may have a smaller shank than specified. Nuances between the actual shank size and the specified size can lead to installation problems. You may struggle to install a traditional bolt in a threaded hole. Even if you’re able to install it, the traditional bolt may fit loosely.

Close tolerance bolts eliminate problems such as these by closely matching their specified size. They have closer shank tolerances than that of traditional bolts. With their close tolerances, they fit more securely in threaded holes. For some fastening applications, traditional bolts may suffice. For sensitive fastening applications in which precision is required, close tolerance bolts are typically used.

Things to Consider When Choosing Close Tolerance Bolts

You should consider the drive type when choosing close tolerance bolts. As the name suggests, this represents the method by which a close tolerance bolt is driven into or out of a threaded hole. Most close tolerance bolts have a recess within their head that supports a specific bit, such as a Phillips head bit.

Something else to consider when choosing close tolerance bolts is the threading. All close tolerance bolts, as well as traditional bolts, have threading. But the way in which the threading is designed may vary. Some bolts have more threading on their shank than others, and some bolts have finer threading than others.

Close tolerance bolts are available in different materials. High-carbon steel is a common material used in their construction. It’s an iron alloy with a high concentration of carbon relative to other types of steel. High-carbon steel is hard and strong, which allows for close tolerances.

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