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Re: Galvanized TC Bolts

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Ken,

Mr. Hunt's observations on twist-off bolts are noteworthy, and I have a few
additional ones.

The tips of ANY twist-off bolt can stick in the end of the wrench if they
get dirty or slightly rusty.  Some 'tip' designs are more susceptible than
others.  This applies to plain finish ones as well.  I see this about once a
week this time of year, and have had it happen to me numerous times while
I'm teaching bolting crews how to use these devices.

Most manufacturers of torque-control twist-off bolts do not galvanize them,
as this makes the torque-tension relationship under which these devices
operate much more difficult to control.  The twist-off bolt is of course a
torque-control based system in which the fastener engineer designs the
system so the break-neck shear element snaps off at precisely the same
torque every time.  (How that level of torque correlates to tension depends
upon many factors ----- but the predominate factors which effect the tension
actually generated are storage and field conditions moreso than manufacturer
production or quality issues.)

In Japan, where these devices are used extensively, use of galvanized
torque-control bolts is not permitted.  You should know also that the ASTM
specification for twist-offs, (ASTM F1852), strictly forbids lubrication or
plating of twist-off bolts by any party other than the original
manufacturer.  Any party that does so would in effect 'become the
manufacturer' and thereafter be responsible for retesting and recertifying
the fasteners as though they were newly manufactured.  (Failure to do so
would also be a violation of the Fastener Quality Act.)

There are a number of sources for twist-offs here in North America.  LeJeune
is among the better known names, although they are not a manufacturer in the
traditional sense of the word.  They have their parts produced in the
facilities of other companies which are willing to apply LeJeune's 'private
label' headmark to the fasteners.  For many years LeJeune's twist-offs were
exclusively produced by Lake Erie Screw Corp in Cleveland, Ohio.  More
recently I gather they have also had their fasteners produced by Infasco and
perhaps by others.  Regardless of the source of supply, ASTM F1852 requires
that all twist-offs be supplied as complete bolt/nut/washer assemblies.
(i.e. not in separate cans)

To resolve any wrench clearance issues, there are special wrenches available
which enable shearing of the break-neck element in rather close quarters.
Some of these are actually hand (rather than electric) operated, and the
greatest variety of these wrenches are available from GWY, Inc. (603)
547-3800.

In my opinion, twist-off bolts are the best system currently available for
efficient tightening of shear/bearing connections.  However, due to common
construction practices, the same can not be said for use of these devices in
slip-critical or full tension connections.  For such connections, use of
either turn-of-nut style 'match-marking' or use of a Direct Tension
Indicator (in addition to the t/o bolt) provides a means to inspect that the
(fixed) torque value used to shear the break-neck was indeed sufficient to
generate specified tension/clamp force.  Unfortunately, contractor
misunderstanding and misuse of twist-off bolts is rampant.


David Sharp
TurnaSure LLC
57 E. 11th St. 8th Fl.
New York, NY 10003


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