could be forced open. Perhaps
Sargent and Greenleaf was the
first US Company to combine a
high security mechanism and
a physically strong lock body/
shackle. The lock in figures 13
and 14, is a re-branded Ingersoll Impregnable from England.
The Lock has the S&G logo and
the Rochester, NY address, an
old lock probably from the late
1960’s. This lock meets all of the
criteria for a high security lock,
but it is not a true U.S. lock.
In 1973 Sargent & Greenleaf
finally invented a good higher
security lock. Not high security
yet, but close. The lock in figure
15, is one of the first. This lock is
cast stainless steel. It was made
by loss wax casting.
Harry Miller, inventor and
past president of S&G, invented
this lost wax casting technique.
The technique is so complex it
will have to be a part of a future
This lock used a Medeco pick
resisting mechanism. It was also
drill resistant and offered key du-
plication protection. There were
a few easily corrected problems
to solve, such as the shackle size.
There were no guarded shackles
at this time.
The lock in figure 16, was
made in 1975. It had a series of
improvements over model “A”.
Perhaps the most significant was
the use of a large shackle and the
introduction of the completely
guarded shackle. These locks
were primarily made for the US
government. A special restricted
Medeco keyway was created
which is still used today.
The S&G lock in figure 17, is
a much heavier version of the
model “C” lock. It has the same
restricted government keyway.
S&G was also producing
guarded shackles padlocks dur-
ing this time. Figure 18, is a typi-
cal completely guarded padlock.
A very formidable lock
A modern lock used by the
government is shown in figure
19. This lock is heavier and
easier to service than the previ-
ous models. It will actually slide
apart into two sections. It uses
the Medeco Biaxial pin system
with a new government keyway.
This lock is dated 1990.
Much of the high security discussion has been about the lock
made by Sargent and Greenleaf.
There were other US companies producing very good locks
during this same time. However,
many of the companies were
small and are not easily recognized.
One lock company was called
The Miracle Lock Co. They made
both partially and fully guarded
shackle padlocks. I don’t think
they made the locks, just re-branded them like S&G did in
their early days. Two different
British mechanisms were used;
the Ingersoll and the Chubb. I
have noted two different companies owning the Miracle Lock
Co. One is Liquidonics Industries
and the other H.O. Boehme Inc.
Observe the different key in
figures 20 and 21.
Perhaps one of the strongest
padlocks ever made was made by
the Hi-Shear Corp. of Torrance,
California. This monster of a padlock is completely cast stainless
18. A completely guarded
14. Cut away Ingersoll.
15. The first model “A” S&G HS
16. Model “C” S&G improved
17. 1983 model much heavier.
19. A modern S&G lock.