--- title: F1554 Anchor Bolt Threads / UNC 1A, 2A, 3A description: "Note: The ASTM document describing Anchor Bolt manufacturing standards if F-1554. The current version is F 1554-07a.   Regarding thread class," image: https://www.thesteelsupplyco.com/hs-fs/file-379584191-jpg/images/f-1554-unc-tolerance-3.jpg --- [![Providing Structural and Miscellaneous Steel Fabricators](https://www.thesteelsupplyco.com/hs-fs/file-14727826-jpg/images/bannerfixed-webrdy.jpg?width=750&name=bannerfixed-webrdy.jpg "Providing Structural and Miscellaneous Steel Fabricators")](https://www.thesteelsupplyco.com/) - [![the steel supply company](https://www.thesteelsupplyco.com/hs-fs/hubfs/logo-1.jpg?width=88&name=logo-1.jpg "the steel supply company")](https://www.thesteelsupplyco.com/) - [![The Steel Supply Co, Inc](https://www.thesteelsupplyco.com/hubfs/top-text-new.png)](https://www.thesteelsupplyco.com/) - [![Specialized Supplies for Structural and Miscellaneous Steel Fabricators](https://www.thesteelsupplyco.com/hubfs/bottom-text-new.png)](https://www.thesteelsupplyco.com/) ![BLOG TheSteelSupplyCo banner950x250](https://www.thesteelsupplyco.com/hs-fs/file-730735349-jpg/images/blog_thesteelsupplyco_banner950x250.jpg?width=760&name=blog_thesteelsupplyco_banner950x250.jpg) ## Steel Manufacturing Blog: Keeping it Steel # F1554 Anchor Bolt Threads / UNC 1A, 2A, 3A Posted on Wed, Nov 13, 2013 @ 10:16 PM - [Tweet](https://twitter.com/share) Note: The ASTM document describing Anchor Bolt manufacturing standards is F-1554. The current version is F 1554-07a.  Regarding thread class, quoting directly from ASTM 1554-07a, "Class 2A shall be furnished when the class is not specified." Typically the prints we see spell out all relevant criteria for bolt manufacturing but rarely mention threading class. As shown above F1554-07a takes care of that but what does 2A mean? In bolt threading the externally threaded item (the bolt) is the A class. The internally threaded nut is the B class. Class indicates tolerance. Class 1 is the loosest fit. It is generally designed for applications where a fast installation is desired and/or the working environment would make tighter fits impractical. An example of the would be for bolts securing concrete forms. Often All Threaded Rod is manufactured to a 1A tolerance. Class 2 fit is the general construction industry standard. It's anchor bolt tolerance is 32% tighter than the 1A fit. This allows for a more secure fit yet still provides enough leeway to accommodate field conditions such as damage or grit in the threads. Properly done, an anchor bolt threaded to a 2A fit can have the usual rust and light contaminants on the threads and still have the nut thread by hand until it bottoms out. The Class 3A is used for machine bolts or other applications where a tighter fit is required. Usually this means the working environment will not create problems in the thread fit, and installation time is not an issue. Tolerance is reduced by 25% compared to the 2A fit. ![F1554 Anchot Bolt](https://www.thesteelsupplyco.com/hs-fs/file-379584191-jpg/images/f-1554-unc-tolerance-3.jpg)The chart to the left (fig. 1) displays how the desired fit is achieved. As the Class goes up the tolerance decreases. Most of the decrease comes from raising the lower tolerance. 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