Six Shooter™
Fastening System
Understanding Fastener
Installation Factors
www.partsmaster.com
TORQUE/BOLT TENSION:
TERMINOLOGY AND RELATIONSHIP
If you have ever had to drill out a bolt or, worse, had to replace a piece of equipment due to a broken bolt, you know about the importance of fastener installa:on and failure preven:on. Understanding fastener installa:on factors significantly reduces the risk of bolted joint failures. In this document, we will discuss terminology, the torque/bolt tension rela:onship, the factors that influence that rela:onship, and remedies to correct those problema:c condi:ons. Also, you will learn how to decipher aspects of a torque chart and determine the bolt tension. Finally, we will discuss how you depend on quality bolts, such as the Partsmaster Six Shooter™ series, that takes all of this into account. The first thing you will want to understand is what torque and bolt tension are, how they are measured, and
how are they related.
Torque is a measurement of how much twisting force is applied when installing fasteners. This is
measured in the form of force and length, stated in pound-feet (lb-ft), or Newton meters (Nm). Common
measurement instruments include torque wrenches and multipliers.
Clamping Force, also called Bolt Tension when specifically referring to fasteners, is the compressive
force that a fastener exerts on the joint. This is measured in pounds (lbs) or newtons (N). Common
measuring devices include load indicating bolts & washers, strain gages, tensioners, and ultrasonic
controllers, among others.
K-Factor is the relationship between the torque and clamping force (or preload). Commonly, it is also
referred to as the “nut factor” and is mistakenly thought of as being the “coefficient of friction”; however, the
K-Factor is really a general-purpose experimental constant. The K-Factor accounts for everything that
affects the relationship between torque and preload – including friction, torsion, bending, plastic
deformation of threads, and many other undesirable conditions that may or may not be anticipated.
Unfortunately the K-Factor is determined experimentally, and wisdom preaches that K-Factors must be redetermined for each new application. In essence, the K-factor accounts for all the other factors that apply in
a fastener assembly outside of the bolt and force exerted on it so it changes from application to application.
There are many unintentional fastener conditions that affect the torque–clamping force (or torque
tension) relationship of a fastener joint. These conditions could cause major clamping force variations
and possibly lead to bolt or joint failure. The bolt having the highest bolt preload tension in an assembly
incurs most of the joint’s load and stresses, and so is the most likely bolt to fail. Making an effort to
reduce clamping force variations in all fasteners in an assembly helps evenly distribute the load and
stress shared by each bolt to prevent joint failures. Just because a torque wrench indicates the bolt was
installed properly, doesn’t make it true!
Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
2
Engineers use clamping force when
looking at the design strength of a
fastened assembly. In a perfect
world with perfect conditions –
using a torque wrench to tighten a
bolt to specific pound feet would
deliver the mathematically predicted
clamping force. Since conditions
are not perfect, torque only gives us
a general indication of the clamp
force or tension. Measuring
clamping force in finished
assemblies is highly recommended
on critical or high tension
applications to make sure the
conditions have not greatly skewed
measurements.
Skidmore-Wilhelm Bolt Tension Tester
One common and easy-to-use instrument for measuring
individual fastener clamping is a Skidmore-Wilhelm Bolt Tension
Tester. Few people use it in the field and do not measure clamping
force in the actual installation. The Skidmore Testers determine
whether or not a specific fastener has a skewed torque-clamping
force relationship before it is used in an assembly.
Skidmore Testers are relatively quick and there are several
videos online that can walk you through the process. Simply install
the bolt into the Skidmore Tester and install the washer and nut.
Use a torque wrench to tighten the nut to the suggested torque. As
you apply torque you can read the measurement of the clamping
force or alternatively, you can read the amount of torque needed to
get the desired clamping force.
Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
3
INSTALLATION CLAMPING FORCE (BOLT TENSION)
COMMON CONDITIONS THAT REDUCE BOLT TENSION
(CLAMPING FORCE) AND HOW TO CORRECT THEM
q  Dinged Male Threads – This occurs in all grades of bolts, especially the large diameters and softer bolt
grades, due to the jostling that occurs during transportation (when bolts are shipped from the
manufacturer, to the plater, to the distributor, and finally to the end user). Remedy: Fully chase dinged
threads with a die prior to installation.
q  Heavy Electroplated Zinc/Cadmium – This may occur at each end of electroplated bolts longer than 3”
and inside electroplated nuts larger than 1/2" diameter (the result of an increase in the eddy current
concentrations that occur during electroplating). Remedy: Fully chase the bolt threads with a die and/or
the nuts with a tap prior to use.
q  Plated Fasteners vs. Non-Plated Fasteners – If both were installed using the same torque and all other
conditions were equal, electroplated fasteners will produce about half the clamping force as non-plated
fasteners. Remedy: Always take into account the fastener finish as a major factor when determining the
installation torque.
q  Dirty Threads – This usually occurs from contact with dirty hands, dirty work areas, or dirty storage areas.
Remedy: Inspect, clean, and dry threads before attempting to install.
q  Rusty Threads – This occurs over time when stored in damp environments. Do not use them or try to
restore them by chasing the threads, as rust eats away the threaded surfaces and alters the thread
dimensions. This will surely skew the targeted clamping force. Remedy: Fastener replacement is required.
q  Female Threads with Dried Thread Locker or Sealer – This usually occurs on equipment having
threaded holes. Remedy: Fully chase the female threads with a tap, flush with solvent, and allow to dry.
q  Dirt or Debris Under the Fastener Heads – This will lower the true clamping force. Remedy: Ensure
there is no debris of any kind under the bolt heads, washers, or nuts.
q  Crossed Threads – This happens when the threads of a bold do not match up with the threads of the nut.
Remedy: If it’s a minor occurrence it can be fixed by fully chasing the bolt threads with a die and/or the
nuts with a tap; however, it is wiser to replace the damaged fasteners if possible.
q  Stripped or Galled Threads – These are extremely unlikely to be fixed by re-cutting the damaged
threads. Remedy: Fastener replacement is required.
q  Gross Misalignment of Parts – This may cause the sides of the bolts to rub against the insides of the
through-holes of a misaligned component attachment. Remedy: Maintain hole alignment during the
installation to ensure the bolts don’t rub the inside of the through-holes. Also, avoid inserting alignment
punches in female threads.
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Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
4
INSTALLATION CLAMPING FORCE (BOLT TENSION)
COMMON CONDITIONS THAT REDUCE BOLT TENSION
(CLAMPING FORCE) AND HOW TO CORRECT THEM
q  Dirty Through-Holes in the Mating Assembly – This may cause the sides of the bolts to rub against the
dirt inside the through-holes of the component being attached. Remedy: Always pre-clean and dry mating
assembly holes.
q  Warped or Unparalleled Joint Surfaces – This will grossly skew the torque and clamping force
relationship. Remedy: The mating part must be re-machined or adjusted to make the component bearing
surfaces parallel prior to fastening the joint assembly.
q  Tightening Sequence – This refers to the order or sequence in which each and every individual fastener
in a multiple fastener assembly is tightened. Failure to recognize and execute the proper installation
sequence will have similar affects as encountered with attaching Warped Mating Parts.
q  Tool Malfunctions – Torque wrenches and multipliers that are damaged or out of calibration could
produce erroneous torque readings that could skew the torque and clamping force relationship.
Remedy: Do not use tools that are suspected to be damaged or are out of calibration.
q  Improper Tool Use Prevention – Users require periodic training on how to use torque wrenches or
multipliers.
q  Tightening the Bolt vs. Tightening the Nut – This will have a significant effect on the final clamping
force. Remedy: Stay consistent and whenever possible, choose to torque the nut, not the bolt.
q  Soft Parts – Female threads tapped into soft metal or non-heat-treated steel will be problematic if the
female thread strength is too much lower than the bolt. This could be a design issue, a result of too many
reinstallations, or a result of over tightening in previous installations.
q  Oversized or Worn Female Threaded Holes – This can occur from over tightening the fastener system
and/or from repeated fastener installation and removal. Remedy: If this situation is suspected, an
engineer should be consulted for corrective action.
q  Under Head Friction – This refers to where the bearing surface of the nut or bolt being turned and
tightened at the point where the fastener contacts the washer or component surface. Softer washers and
surfaces create more friction hardened washers and surfaces and will result in lower clamping loads.
Remedy: All washers in an assembly must be the same type.
q  Blind Holes Not Deep Enough or The Bolt is Too Long – This will create false torque readings.
Remedy: Ensure the fastener length is appropriate to the blind-hole depth. Never drill & tap existing
threaded holes to extend thread run-out. Use a shorter bolt.
q  Never Mix Fastener Grades in a Joint – Unequal or excessive clamping forces could cause failure.
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Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
5
INSTALLATION CLAMPING FORCE (BOLT TENSION)
COMMON CONDITIONS THAT INCREASE BOLT TENSION
(CLAMPING FORCE) & COMMON CORRECTIVE ACTIONS /
OBSERVATIONS
Oil, Wax, and Anti-Seize on the threaded surface area increases the clamping force and must be
factored in when choosing the installation torque to prevent seriously overstressing the bolt.
Oil Coatings which are intentionally applied by the fastener manufacturers, usually to prevent
corrosion in storage, include: 1) Phos-Oil coating, which is usually applied to structural hex bolts, and is of
medium-dark gray to black appearance, and 2) Black-Ox coating, typically applied to hex socket-driven
fasteners, and is of dark gray to black appearance. Black-Ox coating should not have an oil coating but
some manufacturers apply oil to prevent corrosion during overseas shipping.
Wax Coatings are intentionally applied by the fastener manufacturer to ease installation of difficult-toinstall fastener nuts and is generally regarded as desirable. Wax is very difficult to remove, so removal
should not be attempted.
Some examples of where wax is commonly applied to nuts are:
§
Larger diameter (usually ≥ 1/2" diameter) nuts which are stronger than Gr. 8 and could have
either Zinc or Cadmium Electroplating.
§
Some Stainless Steel Nuts to prevent galling or cold welding of the mating threads.
§
Some All-Metal or Nylon Insert Locking Nuts.
Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
6
Anti-Seize - The purpose of Anti-Seize is to
lower installation torque and to reduce clamping
force variations or scatter. It also prevents galling,
which is especially important when installing or
removing stainless steel fasteners. It is also great
at reducing thread corrosion rate and adds
lubricity to prevent fastener seizing during future
removal activities.
Unintended Oil Exposure can occur during
fastener installation. Oil can transfer onto
threads from oily or greasy hands and/or
work surfaces, or as a result of unintended
lubricant overspray. Also, threads that are
chased will usually come in contact with
cutting and tapping fluids.
A great and effective product from
Partsmaster is AS-201 FG. AS-201 FG provides a
K-Factor of 0.16 and has a service temperature
range of -10ºF/-32ºC to 2300ºF/1260ºC. It can be
used in food plants where no food contact will
occur. The AS-201 FG is a white colored product
that is stain resistant.
TORQUE CHART
DETERMINING BOLT TENSION
The primary goal of fastener assembly is to assemble using the correct clamping force. The best
fastener installation scenario occurs when the manufacturer provides specific fastener assembly instructions,
i.e., as found in an included service or maintenance manual. Fastener assembly instructions are usually
provided when critical fastener joints are installed or will require routine or periodic maintenance.
Manufacturer’s technical specifications, service manuals, or drawings always take precedence over
generalized torque charts and general installation guides. When specs, manuals or drawings are not
available, torque charts provide a general guide towards achieving the anticipated clamping force or bolt
tension.
Variables such as bolt grade, bolt coating, prior
service history of the bolted joint, gasket or ungasket joint,
service temperatures, joint design (single shear, double
shear, compression, etc.), joint load (static or dynamic), joint
vibration, corrosion, and how critical the component is in
service must be considered when determining the preload
target ranges, typically as a percentage of the yield strength
of the bolts.
Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
7
TORQUE CHART
Yield strength refers to the specific point where the amount of an applied tension load causes
permanent fastener deformation. The following example scenarios can help you determine the amount of
bolt tension needed:
q  25% of Bolt Yield Strength
§
Unimportant non-gasketed joints exposed to static loads.
§
§
Foundation and anchor bolts under static load.
Joints where fasteners are exposed to serious stress corrosion cracking problems.
q  40% of Bolt Yield Strength
§
Gasketed joints in routine service, including those covered by the ASTM Code, which have not
given any past problems.
q  50 – 60% of Bolt Yield Strength
§
Average non-gasketed joints with normal safety or performance concerns, where past
experience does not suggest higher or lower preloads.
§
§
A good place to start a search for the optimum preload when some trial and error is acceptable.
This is typically the maximum preload for gasketed joints designed to the ASME Code rules.
There will be a few exceptions.
q  70 – 75% of Bolt Yield Strength
§
Upper limit for non-gasketed joints with which past preloads were too low (leaks, self-loosening,
joint slip, joint separation under load or fatigue).
§
Torque control measures must be understood and applied.
q  85 – 95% of Bolt Yield Strength
§
§
Joints having consistent “low preload problems in the past.”
Where the need to avoid failure dictates the use of special techniques such as stretch or
ultrasonic control.
§
Where service loads (or ignorance of service loads) makes it unwise to take the fasteners any
closer to the yield point.
§
May require using specialty tools, techniques and load indicating fasteners.
q  100% of Bolt Yield Strength
§
§
Structural steel bolts tightened by turn-of-nut procedure.
High-performance or problem joints facing self-loosening, fatigue, or other problems where
service loads can be predicted with sufficient accuracy to that the fasteners will not be
ratcheted to rupture later in service.
8
§
Sometimes used in gasketed joints in automobile applications.
§
§
Requires specialty tools and assembly techniques.
May require using specialty load indicating fasteners.
Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
8
PARTSMASTER™
Six Shooter™ FASTENING SYSTEM
The Partsmaster Six Shooter™ Fastening System reduces bolt failure by providing an enhanced
Grade 8 product. They are made in the USA for better craftsmanship and quality. Imported fasteners are
known to have a higher rate of variance from specifications. Knowing where your bolts are coming from
better insures conformance with quality standards. All Six Shooter™ cap screws are completely traceable
with lot numbers and can be traced back to the heat and batch. Six Shooter™s are tougher and less brittle
due to being alloyed with chrominum, nickel, and molybdenum and baked to relieve hydrogen embrittlement
not typically performed by all manufactures but seals the safety and quality. Dy-Cro-Sist plating for ultimate
corrosion resistance reduces the chance of inadvertently reduced clamping force. Cold rolled, not cut,
threads ensure that the threads are just as strong as the head and neck of the cap screw. To give even more
confidence in Partsmaster’s assurance of quality, they have registered with the US Patent and Trademark
office to prevent counterfeiting and has a multi million insurance policy.
Partsmaster has been providing products and
solutions to service the Maintenance, Repair, and
Operations industry for over 40 years. We solve problems
for our customers and help them reduce the total cost of
ownership. Partsmaster, a premier MRO solutions
company dedicated to making its customers’ work easier,
was established in 1968 as a division of NCH
Corporation, a leading provider of industrial goods since
1919. Partsmaster offers intelligent solutions to solve
problems. Our exclusive brands include products you
cannot get anywhere else.
The Partsmaster brands include Cryotool® cutting tools; Dyna Systems® fastener line; Mega Metal®
polymer repair compounds; Trust-X® high productivity abrasives; X-Ergon® welding products; and
Partsmaster Services. Combine our products with sales and service commitment, and Partsmaster is your
knowledgeable, strategic partner that understands your business needs and always takes care of you.
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Six Shooter™ Fastening System
Partsmaster created this guide for training purposes only and assumes no responsibility for the end results of using this guide for
installations. The user must determine torque-tension sustainability independently of this guide.
9
www.partsmaster.com
PARTSMASTER™, A Division of NCH Corp.
P.O. Box 655326 • Dallas, TX 75265-5326
1-800-336-0450
1M504 • © 2015 NCH Corporation
References:
1.
John H. Bickford, An Introduction to the Design and Behavior of Bolted Joints,
2nd Edition, Revised and Expanded, by, Copyright 1990, Marcel Dekker Inc. NY, NY.
2.
SAE Handbook, Volume 1
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