New connector readers often meet the same puzzle. A search result, domain, or supplier catalog carries “M12” in its name, so every part inside it looks like an M12 circular connector. Then a part turns up with a rectangular housing, two PCB-mounted halves, and a pin count meant for a board stack. The label and the hardware seem to disagree. They do not, once the reader separates a category name from a company or site name. The practical question is simpler: what touches what when the connector mates? This explanation focuses on that question, using a 32-pin board-to-board waterproof connector as a concrete reference point without turning every part with a familiar name into the same product family.

M12 CONNECTOR