Redesign of 1500/1525

Hello, all, especially those vendors of Master Lock Company products for
many years. Does anyone know when Master Lock modified the innards of
their 1500/1525 locks such that a steel spring/band returns the
bolt/plunger assembly to the locked position when the shackle is raised?
The older design (available in the 1960s up to ..?) used a cam coaxially
mounted with the disc tumblers to achieve this action. I think this also
coincides with redesign of the tumbler discs such that the last number of
the combo cannot be conveniently discovered by pulling on the shackle
while turning the dial. The older design is easily identified by the
knurled silver knob on the rotary dial.
I've done a patent search at USPTO but only came up with patents on Soref
and Foote's original "permutation" key/combo lock designs (assuming Master
patented the modifications). Thanks for your time and comment.
John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337
Reply to
J. B. Wood
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