Do you need a crash course on type balls?
The lever on each type ball is usually black. Only those with a specially character will have a white lever. This is to help distinguish between two type balls bearing the same type name but differing in this one respect.
On top of each type ball there is a triangle which points toward the platen whenever the typewriter is in lowercase position. A solid triangle denotes 10-pitch type, a hollow triangle 12-pitch type.
Your Selectric can either be 10 (pica), 12 (elite) pitch or both. If you are unsure look at the ruler in the front of your machine. Here you’ll see the pitch as well as either a hollow triangle or solid triangle depending on pitch.