The principal type of volcanism on Mars is almost certainly basaltic too.

The 24 cases represented the principal types of cancers cited.

There are two principal types of color screens for lightweight portables.

There are two principal types of basis construction methods.

But among the six principal types of military satellites some were stretched dangerously thin.

Other designs are a compromise between the two principal types.

Regarding sound generated inside the building, there are two principal types of transmission.

There are two principal types of entries in the database.

These form the three principal types on which all capitals are based.

However, probably the K-type can be regarded as the principal type.