Molex terminal block is the vernacular term for a two-piece pin and socket interconnection, most frequently disk drive connectors. Pioneered by Molex terminal block Company, the two-piece design became an early electronic standard. Molex developed and patented the first examples of this connector style in the late 1950s and early 1960s.[1][2] First used in home appliances, other industries soon began designing it into their products from automobiles to vending machines to mini-computers.

In such a connector, cylindrical spring-metal pins fit into cylindrical spring-metal sockets. The pins and sockets are held in a rectangular matrix in a nylon shell. The connector typically has two to 24 contacts and is polarized or keyed to ensure correct orientation. Pins and sockets can be arranged in any combination in a single housing, and each housing can be either male or female.

There are three typical pin sizes: 1.57 mm (0.062 in), 2.36 mm (0.093 in), and 2.13 mm (0.084 in). The 1.57 mm pin can carry 5 A of current, while the 2.36 mm can carry 8.5 A. Because the pins have a large contact surface area and fit tightly, these connectors are typically used for power.

This style of connector was first used as a computer disk drive connector in the late 1970s, initially on the Shugart floppy disk drive as well as Atari (1979) on its path to becoming a de facto standard. It is in this role that the vernacular term Molex terminal block is most frequently used. AMP (now a division of Tyco International) developed the MATE-N-LOK 2.13 mm pin connector that is the same as the Molex 8981 power connector. This Molex and Amp connector configuration was the established standard for disk drive power connectors until the introduction of SATA disk drives.