Tension wrench (as used in lockpicking):
The tension wrench (sometimes called a "torsion
wrench" or "torque wrench"), occurs as one of the
two basic tools of lockpicking. Contrary to a
literal interpretation of the name, such a device
does not "stretch" anything(1). Quite
the opposite, it exists as a tool allowing the user
to exert a small amount of torque about the
longitudinal axis of an object running
perpendicular to the wrench itself. For this
reason, the name most likely comes from a corruption of the
rarely-used "torsion wrench", which more accurately
describes the actual purpose of such a device.
A tension wrench generally looks like this:
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Basically, a thin (and stiffer works better) strip of
metal, approximately 5 inches long by an eighth of an
inch wide, with a 70-85 degree bend near one end. The
head (the short portion past the bend) should measure
roughly half of an inch long.
The tension wrench exists for one reason and one
reason only. It allows the user to put a slight
amount of torque on the plug (aka core, aka cylinder,
aka the thing that actually turns when you put a
legit key in). This causes one or more driver pins
(the ones above the plug, in the hull) to bind (catch
between the plug and the hull) which in turn
allows the user to attempt to pick the lock by
raising each pin to the sheer line one at a time.
To quote the MIT Guide to Lockpicking (the Bible on
this subject), which refers to the tension wrench
by the more apropos name of "torque wrench",
People underestimate the analytic [sic] involved
in lock picking. They think that the picking tool opens
the lock. To them the torque wrench is a passive tool
that just puts the lock under the desired stress.
Let me propose another way to view the situation.
The pick is just running over the pins to get
information about the lock. Based on an analysis of
that information the torque is adjusted to make the
pins set at the sheer line. It's the torque wrench
that opens the lock.
1 - For certain precision fastening
needs, something worthy of the label "tension" wrench
does exist. These always require hydraulics due to
the nature of the task of literally putting a
bolt under tension rather than merely securing it,
under some arbitrary degree of tension, via friction.
Such devices generally carry much fancier names than a mere
"wrench".
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