Does Portland Bolt produce bolts with a Class 3A thread? What does the “A” mean in “3A”?

Portland Bolt does not manufacture or supply bolts with a Class 3A thread. Instead, Portland Bolt manufactures and supplies bolts with a Class 2A thread and nuts with a Class 2B thread. The A designates a male thread and the B designates a female thread.

Essentially there are three different classes of threads, the difference being the precision with which the fasteners are threaded. Class 1 threads are a loose thread fit typically specified for quick assembly/disassembly or for environments where dirt or contaminates may interfere with tighter threads. This class of thread is exceedingly rare, and from Portland Bolt’s collective experience, is virtually never specified or requested. The vast majority of fasteners in the marketplace, and the only thread class that Portland Bolt manufactures, are Class 2 threads. Class 2 threads offer the perfect mix of function and strength, but also efficiency and manufacturing economy. Nearly all construction and industrial fasteners from structural bolts to anchor bolts have Class 2 threads. Both ASTM and SAE specifications designate a class 2 tolerance. Class 3 threads are tight tolerance threads that have no allowance and have very tight tolerances. Class 3 threads are often specified for tight tolerance fastener applications in critical use situations where safety and strength are a primary concern, such as the aerospace industry. Portland Bolt cannot manufacture a Class 3 thread with our bolt manufacturing equipment and a Class 3 thread fit must be created by a machine shop with precision machinery.

Written

2 comments

    I have a technical question regarding the fit of a 3A screw thread, how will this fit on a 2B internal thread, and is this a standard practice in the industry?

    please advise, thank you.

    @Jorge- A 3A screw should tap in just fine to a 2B threaded hole. We don’t know if that is standard practice, as we do not get involved on the design end, and also do not typically handle 3A products.

Leave a Reply to Dane McKinnon Cancel reply

Your email address will not be published. Required fields are marked *