How it connects
Push-fit insertion where the male pin's spring leaves compress inside the recessed 4 mm brass/copper tube, while the plug and socket insulating plastic shrouds overlap to prevent accidental contact with live metal.
Male and female halves
Female socket/jack; mates with a male shrouded or unshrouded 4 mm banana plug (test lead).
Usually connects to
- Male banana plug of matching nominal diameter and insulation style, including stackable types
- 4 mm safety plug with fixed or retractable shroud, only where the socket accepts that shroud
Common sizes
- Nominal 4 mm (0.16 in) contact diameter; 2 mm miniature test-lead versions also exist.
- Typical shroud OD about 11–14 mm and contact depth about 15–20 mm; these are not established dimensions for every 4 mm speaker jack.
Where it is used
electronic test and measurement equipmentdigital multimeters and clamp meterslaboratory power supplies; lab power supplieseducational physics and electronics benchesspeaker and amplifier terminals; Speaker and amplifier wiringeducation/lab kitsAudio wallplate connectionsElectrical test connections
Variations
- Panel/chassis threaded mount
- PCB safety socket
- Right-angle test-lead or cable socket
- Unshrouded jack
- IEC 61010 shrouded safety socket
- Socket built into a binding post
- Female-female keystone coupler
- Related 2 mm miniature safety socket
How to recognise it
A circular plastic front housing with an internal concentric annular groove surrounding a deeply recessed metallic 4 mm tube, preventing finger or accidental contact.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| Unshrouded 4 mm banana jack / binding post | Unshrouded jacks lack the raised outer plastic insulating barrel, leaving bare metal or a flush face that exposes live conductor surfaces. |
| 2 mm miniature shrouded banana socket | 2 mm sockets have a significantly smaller internal bore (2 mm vs 4 mm) and compact shroud. Bore is about half the diameter; 4 mm plugs won't enter. |
| Shrouded 4 mm safety socket | Safety sockets have an insulating sleeve around the contact so only shrouded plugs fully mate; plain jacks have exposed metal at the opening. |
| Binding post bare-wire terminal | The banana plug enters the axial front opening. Bare wire instead enters a side hole and is secured by tightening the post cap. |
| Female threaded fitting | A banana socket is an electrical contact accepting a straight pin; mounting or cap threads do not define its plug mating interface. |
Also called
4mm shrouded banana jacksafety banana socketsheathed banana jacktouch-proof banana socket4mm safety socket4 mm socketbinding post (when combined with a screw terminal)
Good to know
Mandated by safety standards such as IEC 61010 on test equipment (multimeters, clamp meters) to provide high voltage CAT II/III/IV touch protection during testing.
Related connections
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