The regular bush is a far less complex piece, with only
one variant available. It can be used for securing axles or
maintaining 1-stud spacings. One of its sides is smooth,
and the other has four small notches in it. The notches fit
LEGO studs and enable the bush to be placed in the middle of
4 studs, as shown in Figure 4-14. That means the bush can
be connected to bricks and plates sized 2×2 studs or larger.