LEGO Technic turntables come in big and small versions.
There are two variants of the big one, with the only real difference being the fact that the older style (left) is suited
for studfull constructions, while the newer one (right) is
suited for studless ones. Additionally, the older one is 4 studs
tall, and the newer one is 3 studs tall. The outer ring of both
turntables has 56 teeth. The inner one has 24 teeth and is
the exact size of the 24-tooth gear; however, the construction
of the studless turntable makes it impossible to put a
24-tooth gear inside it. Still, a turntable can be meshed with
smaller gears.
Both variants consist of upper and lower halves, which
can get separated if sufficient force is applied. The outer
ring is most often driven by an 8-tooth gear or a worm gear.
The turntables can be used in a normal or an upside-down
position (the studless one is better suited for an upside-down
position), depending on whether we want to drive them from
above or below.
As of 2012, a small turntable has been introduced. It
consists of two halves (see Figure 5-23), each with two pin
holes, and it has a ring of 28 teeth attached to one of the
halves. One side of the teeth is chamfered, as in bevel gears,
and the other one is unaltered, as in straight-cut or spur
gears. Therefore, the turntable can be engaged by bevel
gears only from the side of the toothless half, as shown in
Figure 5-24. The combination of gears that can be used with
this turntable is limited, with the single- or double-bevel
12-tooth gear clearly being the best-suited one.