ASME B18.5 (2012)

Round Head Bolts (Inch Series)

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Annotation and contents

This Standard covers the complete general and dimensional data for the various types of inch series bolts generally classified as round head bolts and recognized as an American National Standard.

The key types of bolts covered include:

  • Round head bolts are frequently used in rail, heavy equipment, and agricultural applications.  The bolts have a low profile head that does not interfere with many applications where a dramatic protrusion from a hex head or other style would.  There are a variety of styles that include underhead features to hold the bolt in place while a nut is being tightened.


  • Step bolts are of similar design to a round head, square-necked bolt but with a much larger head size.


  • Elevator bolts are of similar design to the round head bolts but with a comparatively flat head frequently used in agricultural applications such as grain and other such elevators

ASME B18.5-2012 requires the use of additional standards – published by ASTM, ASME, IFI, and SAE -- in reference to thread dimensions, materials, mechanical properties, and finishes. 

Intended for those involved in the design, manufacture, use, or maintenance of round head bolts and ancillary components. 

My organization refers to this Standard to ensure
continuity and uniformity in our product offering.
– Chris B Williamson, Director of Quality
 Fastenal Company

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