[SML] Thread projection

[Loren Schreiber]

Greetings,

I'm looking for a published standard for the number of threads that are 
required to project beyond the end of the nut--especially Nylocks.

I've always recommended 1.5 to 3 threads extending beyond the nylon 
insert, or the face of a metal nut. But when I tried to find an actual 
standard to cite, there were none related to our industry and only a 
few, rather specifically for "flanged joints: *ASME B31.3, 335.2.3.
"*

This is the best I could find on the web:

This is a difficult question to answer. Depending on your application, 
the answer could be anywhere from 1/2 engagement, up to having two full 
threads extend beyond the nut. Look at these conflicting answers found 
in four separate technical publications.

Federal Highway Administration, "Guidelines for the Installation, 
Inspection, Maintenance and Repair of Structural Supports for Highway 
Signs, Luminaires and Traffic Signals." Section 16.3.1.2 Anchor Rods
"Many times the rod is not long enough and the anchor nut is not fully 
engaged. This in itself is not a serious deficiency as long as at least 
three quarters of the nut is engaged."
http://wwwcf.fhwa.dot.gov/bridge/signinspection.pdf

Industrial Fasteners Institute, Joe Greenslade, Director of Engineering 
Technology.
"How Many Threads Should Be Beyond The Nut?. The answer is: A minimum of 
two thread pitches should extend beyond the top surface of the nut."

RCSC (Research Council for Structural Connections) Specification for 
Structural Joints Using ASTM A325 or A490 Bolts 2.3.2. Geometry
"Heavy-hex structural bolt dimensions shall meet the requirements of 
ANSI/ASME B18.2.6. The bolt length used shall be such that the end of 
the bolt extends beyond or is at least flush with the outer face of the 
nut when properly installed."
http://www.boltcouncil.org/files/2009RCSCSpecification.pdf

AISC Design Guide1 Page 10 Section 2.11.3
"Often, when the anchor rod is short, it may be possible to partially 
engage the nut. A conservative estimate of the resulting nut strength 
can be made based on the percentage of threads engaged, as long as at 
least half of the threads in the nut are engaged."
http://www.aisc.org/store/p-1749-design-guide-1-base-plate-and-anchor-rod-design-second.aspx

AISC Steel Construction Manual, 13th Edition, Section 14-10
"Adequate thread engagement for anchor rods is identical to the 
condition described in the RCSC Specification as adequate for steel to 
steel structural joints using high strength bolts: having the end of the 
[anchor rod] flush with or outside the face of the nut"
- See more at: 
http://www.portlandbolt.com/faqs/recommendation-on-thread-engagement/#sthash.DV9RwF3K.dpuf

I believe common practice in theatre is 1.5 to 3 threads, but I'm not 
sure how much weight that carries with lawyers and such.  What say you all?

Loren

-- 
Professor Loren Philip Schreiber
Technical Director
School of Theatre, Television, and Film
San Diego State University
ETCP-T Certified Rigger #1095
CA Contractor License #966080


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