These odd and colorful gears are parts of two early systems
of LEGO gears: the Samsonite system introduced in 1965
and the Expert Builder system introduced in 1970. They are
predecessors of today’s Technic system, which replaced them
in 1977. These gears have been absent from LEGO sets since
then, but they’re still relatively easy to find in secondhand
sales. They mesh in both a parallel and a perpendicular
manner but only with the gears from their own group. Just
like knob wheels, they have teeth that make them work
unevenly. Note that they are massive and made from very
durable material, and some even have metal centers, which
makes the smallest of them popular with builders seeking
heavy-duty gears. The larger ones are rarely used because
of their enormous size.