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How
many of us think about the condition of our pulling hardware before we
use it. Or how that
hardware is supposed to be used. I
can’t count the number of times I have seen shackles misused on the
trails. People put a lot of
trust in a piece of hardware that if misused can cause a catastrophic
incident. In the next few
paragraphs I will discuss how to determine the size and capacity of
shackles and how to rig them properly before pulling either yourself or
someone else.
Size
The size of a shackle is determined by the diameter of the beam (A).
It is not determined by the diameter of the pin.
Most shackles have the diameter stamped on them.
If not, use a tape measure to estimate the size
Screw
Pin Shackles
|
|
Dimensions-Inches
|
Max. Load Tons
|
|
Size
Dia.
|
Pin
or Bolt Dia.
|
|
7/16
|
1/2
|
1 ½
|
|
1/2
|
5/8
|
2
|
|
5/8
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3/4
|
3 ¼
|
|
3/4
|
7/8
|
4 ¾
|
|
7/8
|
1
|
6 ½
|
|
1
|
1 1/8
|
8 ½
|
|
1 1/8
|
1 1/4
|
9 ½
|
|
1 1/4
|
1 3/8
|
12
|
Capacity
When
tested all shackles are pulled at a uniform rate of speed in a direct
tension. Any deviations
such as angular lifts, shock loads, modification of the basic forging
etc. will result in drastically reduced maximum loads.
In many cases, if a shackle is not pulled with even pressure on
the pin and the upper portion of the shackle the capacity can
be reduced by as much as 70%.
In other words, if it’s not used correctly a shackle rated for
6 ½ tons can be reduced to less than 2 tons.
Rigging
So
what is the correct way to use a shackle?
In most cases you want to have the strap applying even pressure
to the pin. The object is to keep from applying point pressure to any part
of the pin. The only reason
you should turn the shackle around is if your shackle mount is wide
enough to apply even pressure
to the pin.
Summary
When choosing a shackle make sure it will fit your application.
It is unlikely that a winch would rip a shackle in half.
But put that shackle in a situation where that vehicle is stuck
behind a rock with the shackle not properly positioned and you could be
looking a missile. Most 3
and 4-inch straps have higher capacities than a 7/8-inch shackle.
So use caution when using shackles or any other pulling hardware.
If a shackle is misused, it will happen sooner or later.
Next month I will talk about straps. |