Mike was familiar with the old locking liner design patented
by Watson & Chadwick in 1906 for Cattaraugus. Used first on
traditional folding hunters, this mechanism became standard on
electricians' pocketknives, and was also used on Cub Scout
knives. In this design, the liner projects above the handle, and
it is split lengthwise, alongside the pivot pin. The side of its
narrow tip engages the front edge of the tang when the locked
blade is open.
Mike noted that only a thin extension of the liner could be
used as the lock in the Watson & Chadwick design. This was
because most of the liner had to engage the pivot pin, in order
to hold the knife together against the tension of the backspring.
The result is that this type of lock is inherently weak.
Mike went back to first principles. He realized that if
spring tension and lock-up could be provided by a liner alone, he
would be able to dispense with the backspring entirely. With the
back spring gone, he could then have the end of the liner cut-out
engage the bottom end of the tang, making for a much stronger and
more positive lock. Indeed it would be nearly as strong as the
old Marble's Safety folder (patented in 1902), while dispensing
with that knife's long, awkward, and fragile fold-up extension
guard (the folded guard serves as that knife's lock when the
blade is opened).
