A binding post is a connector commonly used on electronic test equipment to terminate (attach) a single wire or test lead. They are also found on loudspeakers and audio amplifiers as well as other electrical equipment.
A binding post contains a central threaded metal rod and a cap that screws down on that rod. The cap is commonly insulated with plastic and color-coded: red commonly means an active or positive terminal; black indicates an inactive (reference or return) or negative terminal; and green indicates an earth (ground) terminal.
Commonly designed in a style called five-way or universal, such binding posts allow the connection of several different types of connections:
- Banana plugs, inserted into the open end of the binding post
- Pin connectors, inserted into a hole drilled through the metal post and clamped by the screw-down portion of the binding post.
- Bare wire inserted through the same hole and clamped, or
- Wrapped around the metal post and clamped.
- A lug terminal, with a 1/4-inch (6.35 mm) inner diameter, inserted around the metal post and clamped.
The binding post was a commercial invention of the General Radio Corporation.
Even so-called isolated binding posts are typically not sufficiently isolated to protect users from coming into contact with their metal parts carrying voltage. As such they are not suitable to be used for carrying dangerous voltages (cf. extra-low voltage). On several types of equipment it has been becoming common to no longer use the traditional binding posts, but safety banana jacks. The universal property of binding posts is lost here, since safety banana jacks can only be used with traditional and safety banana plugs.
In the past, it was common for multiple five-way binding posts to have their drilled holes lined up; this provided convenience in some applications as a bare wire could be strung from post to post to post. But this also impaired safety as two wires or pin connectors could be inserted from opposite sides of two binding posts and the tips of the wires or probes might inadvertently short together. Holes are now normally aligned in such a fashion that such shorts cannot occur.
In order to permit the use of double banana plugs, the distance between the positive and negative plugs should be 3/4 inch (19 mm).