There are many types of connectors used to connect electronic circuits to each other and the outside world. Some of the most common are shown below.

The Fahnestock clip is mostly obsolete but is still used in classrooms for demonstration circuits. Banana plugs are still widely used.

RCA connectors are sometimes called phono connectors because they were commonly used to connect phonograph turntables to amplifiers. RCA connectors typically connect to shielded cable (the center conductor surrounded by a cylindrical shield conductor). A disadvantage of the RCA connector is that the center conductor makes contact before the outer conductor. Without the outer shield connected, noise, often a lot of it, enters the circuit for the short time before the outer conductor is connected. In audio systems, this causes a loud buzzing in the speakers. Phono connectors are not to be confused with phone connectors, which were widely used for telephone exchange switchboards (1/4-inch standard version). Many phone jacks have built-in switches that switch a circuit to the plug. For example, with the plug out sound signals go to a speaker. When the plug is inserted into the jack, the speaker is automatically disconnected and the signal is routed to the headphones through the phone plug.

The right image above has binding posts (wires are threaded through the holes then the knobs are tightened onto the wires). The binding posts are also banana jacks and can accept banana plugs in the ends. The holes in the side of the adapter also accept banana plugs. All this adapts to a BNC connector.

The BNC connector (Bayonet Neill-Concelman) is named for its designers, Paul Neill (Bell Laboratories) and Carl Concelman (Amphenol). It is a shielded connector like the RCA connector but has a controlled characteristic impedance (something you will learn about in communication circuits). It also has a locking “bayonet” mechanism. To disconnect it you have to push then turn it.

The D-sub connector is named for the shape that is similar to the letter “D.” It is mistakenly called a DB connector in some computer circles. Hewlett-Packard calls the 25-pin version the DB-25 and this was picked up in the computer industry. HP calls no other version of the D-sub connector a “DB” connector.

Blade connectors come in several styles such as spade lugs (flat or forked), bullet lugs and ring lugs.

Coaxial power connectors come in various sizes that are incompatible with each other. Connectors for higher voltages are often chosen so that they cannot be plugged in to lower voltage devices.

The Molex connector (four-pin version shown) was patented in the 1960s. The similar, but incompatible AMP connector is usually called a Molex connector by mistake. Each pin or receiver is crimped to an individual wire then inserted into the connector shell where it snaps into place. The AMP connector was the power connector of choice for hard disk drives in computers for many years (and always called a Molex connector).