The classification of connector products can be somewhat confusing, but from a technical perspective, there are two basic methods of classification:

1. Based on the physical structure: circular and rectangular (cross-section).

2. Based on the operating frequency: low frequency and high frequency (with 3MHz as the boundary).

According to the above classification, coaxial connectors belong to the circular category, while printed circuit connectors belong to the rectangular category (historically, printed circuit connectors were indeed separated from rectangular connectors to form a distinct category). Popular rectangular connectors have a trapezoidal cross-section, which is approximately rectangular. The division of low frequency and high frequency based on the 3MHz boundary aligns with the frequency division of radio waves.

In addition to the basic classification principles mentioned above, connectors can also be further classified based on their purpose, installation method, special structure, and special performance. These classifications often appear in publications and manufacturer's promotional materials, but they generally serve to highlight specific features and uses, without going beyond the basic classification principles mentioned above.

Considering the technological development and practical considerations of connectors, they can be further classified into the following categories based on their universality and relevant technical standards:

1. Low-frequency circular connectors: mainly used for low-frequency signal transmission, with a circular physical structure.

2. Rectangular connectors: characterized by a rectangular (cross-section) physical structure, widely used in various fields.

3. Printed circuit connectors: specifically used to connect electronic components on printed circuit boards, forming a separate category separated from rectangular connectors.

4. RF connectors: used for high-frequency signal transmission, suitable for RF equipment and communication systems.

5. Fiber optic connectors: used in fiber optic communication systems to facilitate the transmission and connection of optical signals.

These classifications of connector categories help to better understand and apply different types of connectors.