This particular combination was developed as a
convenience for the official LEGO Technic sets. Large and
complex sets are very often divided into several modules
that are built separately and then connected. The bush
with a long pin is well suited for this task because it can be
pushed in and pulled out more easily than regular pins (see
Figure 4-16). LEGO uses this piece for temporarily locking
some modules together as well: For example, the bush with a ong pin enables a truck’s cabin to be lifted up, lowered back,
and then locked in that position (as shown in Figure 4-17).