How it connects
Plug is pushed straight in; the plug's hollow sleeve slides over the jack's centre pin while a spring contact grips the plug's outer barrel. Held by friction only, no latch or seal (some panel jacks have screw-on caps).
Male and female halves
This is the female half (jack/socket, with a centre pin inside a bore). The male half is the barrel plug (hollow cylinder). Polarity varies; centre-positive is most common.
Usually connects to
Common sizes
- Named by plug OD × pin diameter: common 5.5 × 2.1 and 5.5 × 2.5 mm; also 3.5 × 1.35, 4.0 × 1.7, 2.5 × 0.7 and 6.3 × 3.0 mm.
- Plug lengths are typically about 9–14 mm, with many listed at 9.5–12 mm. A 5.5 × 2.1 mm estimate does not establish the specific product size.
Where it is used
consumer electronics; hobby electronicslow-voltage DC appliancesCCTV camerasLED lightingrouters and small devicesrechargeable deviceshumidifiers/diffuserssmall appliances powered by wall adapters
Variations
- PCB mount
- Threaded panel mount with nut, including M8
- Inline/pigtail
- Screw-terminal adapter
- Switched third contact
- Locking/waterproof
How to recognise it
A round hole, usually 5-6.5 mm across, with a single metal pin in the centre, on a device housing, PCB or cable end; often labelled DC IN or with a voltage and polarity symbol (circle with + / - showing centre polarity).
Often confused with
| Confused with | How to tell them apart |
|---|---|
| 5.5x2.5 mm barrel jack | Same 5.5 mm bore but thicker 2.5 mm centre pin; a 2.1 mm plug fits loosely or not at all. Measure the pin. Looks identical; center pin 2.5 mm vs 2.1 mm. A 2.1 plug won't fit a 2.5 pin; a 2.5 plug fits a 2.1 pin loosely. |
| 3.5 mm audio (TRS) jack | Audio jack is an empty hole with no centre pin; barrel jack has a visible pin in the bore. Audio jack has no center pin; plug is a solid pin with rings. Audio jack has no centre pin; the plug is a solid tip with ring bands. |
| EIAJ connector | EIAJ plugs have a different dimension set defined by voltage class; sizes look similar so measure. |
Also called
DC power jackDC barrel jackcoaxial power connector (socket)5.5x2.1 mm DC jackDC inletDC-099 / DC-005 jackDC female pigtail
Good to know
A 5.5 × 2.1 mm barrel connection can look indistinguishable from 5.5 × 2.5 mm. Check size, ratings and polarity separately.
Related connections
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