Recommended Nut Engagement
Question: Larry, with a steel fabricator in Alabama asked, “After the column has been tightened down to the anchor bolt, how much thread is supposed to be left on the bolt?”
Answer: This is a common question that applies not only to anchor bolts, but other construction fasteners as well. According to page N-66 of the 7th edition of the Industrial Fastener Institute manual, “To guarantee full length of thread engagement with a nut, bolt length should permit a length of two thread pitches to protrude beyond the nut face following tightening. For structural bolts, refer to the 2000 Research Council on Structural Connections (RCSC) Bolt Specification in the 3rd Edition LRFD Manual which states:
“Sufficient Thread Engagement—having the end of the bolt extending beyond or at least flush with the outer face of the nut; a condition that develops the strength of the bolt.”
