This is the smallest LEGO gear in existence, and it’s a fragile
one. It’s not suited for high torque, but due to its size, it’s
very popular, especially for gearing down. The 8-tooth gear
has the disadvantage, however, of generating extremely
significant backlash.
There are at least three variants of this gear coming
from three slightly different molds (shown in Figure 5-14).
The initial variant of the 8-tooth gear has thin teeth around
a thin central ring, which is called back iron. The later, middle
variant has the same central part, but its teeth are shorter,
thicker, and presumably stronger. The third variant is the one
most sought after, but it is unclear when it was in production
and in which sets it was included. It maintains the shape of
the teeth introduced in the middle variant, but its central
part has an extra layer of material between the teeth, adding
to its thickness. This change is clearly intended to prevent
the teeth from bending under torque, thus making the entire
piece significantly stronger.