The specification states that if no thread pitch is specified, the anchor bolt should have Unified National Coarse (UNC) threads, which is the standard construction grade thread pitch, with a standard Class 2A thread dimensional tolerance. ASTM F1554 mentions both Class 1A and Class 2A dimensional tolerances, but defaults to the standard Class 2A tolerance, if nothing is specified. ASTM F1554 does not at any point mention Unified National Fine (UNF) threads or the tight tolerance Class 3A thread dimensional requirement and thus Portland Bolt will always assume that UNC coarse threads are required unless our customer or a drawing specifies another thread pitch.
Virtually all F1554 anchor bolts are manufactured with UNC coarse threads, but on the rare occasion when 8 UN threads are required they will be specified on the plans by an engineer. The F1554 specification does mention 8 UN threads as a potential option in diameters above 1” diameter, but in Portland Bolt’s collective experience it is exceedingly rare to see 8 UN threads on a F1554 anchor bolt being specified or required on drawings. ASTM F1554 also does not mention metric diameters in the most recent version of the specification, but also does not prohibit metric diameters. However, the availability of metric round bar in North America is very limited and most anchor bolt manufacturing companies in the United States are not tooled up to produce metric F1554 anchor bolts cost-efficiently. If a metric diameter F1554 anchor bolt is specified or shows up on a drawing, the contractor should work with the Engineer of Record to determine if it is feasible to use a soft conversion to the closest Imperial size.
11. Thread Dimensions
11.1 Uncoated Anchor Bolts:
11.1.1 Unless otherwise specified, threads on Class 1A and 2A anchor bolts shall conform to Class 1A and 2A, Unified Coarse Thread Series of ASME B 1.1, respectively. When an anchor bolt class is not specified, Class 2A shall be furnished.
11.1.2 For diameters above 1.0 in, a purchaser may specify threads conforming to Class 2A, 8 UN Thread Series of ASME B1.1.