The metal “cobra head” wheel guard modification (1956)
In 1956 the slim models had
a metal “cobra head” wheel
guard modification located
in the chimney behind the
flint wheel. The guard was
placed in this position in
order to prevent the flint
wheel from getting too hot.
Unfortunately, this piece of
metal did not hold up over
time and Zippo found that
the wheel guard caused
problems in lighting the wick.
Only one year later Zippo
broke off all the wheel guards
from its remaining inside unit
inventory and moved the
wick 1/32 of an inch further
away from the wheel. Later
in 1957 Zippo produced all
slim inserts without guards. 

The bottom stamp was used
from 1956 up to early 1958.
The lower right "10 K G.F."
stands for 10 karat gold filled.

But there are some more differences between a true 1956 slim and the later releases.
The sixteen hole 1956 slim size insert
has a dimpled chimney and a smaller
hollow wheel rivet holding a smaller
flint wheel than the regular Zippo
lighters from the same era.

The 1956 cam had an hour glass 
shape with sharp corners and the
chimney shows a different cut out
than later produced slim inserts.

Only the inserts from 1956 had "PAT.2517191" and "PAT. PENDING" on them.
a 1956 silver filled "comet" design
PAT. 2517191 ® PAT. PENDING
The new material added to the
product line in 1955, the silver
 filled & rhodium plated cases
(which prevented tarnishing)
was used on slim Zippos too.
Already within the first year
of production the slim Zippo
lighters were available in 10K
gold filled & silver filled.
The10K gold filled models
were Stars, Rope and Scroll

designs.
The silver-filled models were

Comet, Feather and Ribbon
designs.
As can be seen on the left
the“cobra head” wheel guard
shows some corrosion due
to usage and many of the
guards broke off on their
own which was a reason
too for Zippo Mfg. Co. to
change the inserts in 1957.