How it connects
Plug pushes into the jack; the jack's center pin enters the plug's bore and a spring contact grips the outer sleeve. Held by friction only, no lock or seal (some versions have a locking ring).
Male and female halves
This is the plug (male, on the cable) even though its center is a hollow socket. The mating half is the jack (female), which has the center pin. Center is usually positive on most adapters but polarity is not fixed.
Usually connects to
- Female DC barrel jack of matching outer diameter and pin/bore size, such as 5.5 × 2.1 mm
- Inline female barrel connector of the matching size
Common sizes
- Named by sleeve OD × bore ID: common 5.5 × 2.1 and 5.5 × 2.5 mm; also 3.5 × 1.35, 4.0 × 1.7, 4.8 × 1.7 and 2.5 × 0.7 mm.
- Shaft length commonly 9.5–14 mm, often 9.5–12 mm. Match the bore to the mating pin; 2.1 and 2.5 mm versions are different fits.
Where it is used
consumer electronics power adaptersCCTVLED stripsrouterssmall appliances and battery chargerswall-wart power adapterssmall appliances and controllers
Variations
- 5.5x2.1 mm; 4.0x1.7 mm; 2.5x0.7 mm
- 5.5x2.5 mm; 3.5x1.35 mm
- EIAJ (JEITA RC-5320A) sizes
- IEC 60130-10 types
- right-angle plugs
- locking screw-ring plugs
- solder-tab, screw-terminal and push-terminal field plugs
- center-positive vs center-negative polarity
How to recognise it
Short smooth metal tube at the end of a power cord with a hollow center that often has a plastic insert (sometimes yellow or white). There are no threads or ridges. Look for a polarity symbol and an output rating on the power adapter label.
Often confused with
| Confused with | How to tell them apart |
|---|---|
| 5.5x2.5 mm barrel plug | Same outside diameter; only the bore differs (2.1 vs 2.5 mm). Check the label or measure the bore; a 2.5 mm plug on a 2.1 mm pin makes a loose connection. |
| 3.5 mm audio (TRS) plug | An audio plug is a solid pin with insulating rings; a barrel plug is a hollow sleeve. |
| RCA plug | An RCA plug has a protruding center pin inside a split outer shell; a barrel plug has no pin, only a bore. |
| 5.5x2.5 mm vs 5.5x2.1 mm barrel plug | Same outside diameter; the 2.5 mm bore fits loosely on a 2.1 mm pin. Measure the bore or check the label. |
| NEMA 1-15 mains plug | NEMA plugs have flat blades for AC mains; a barrel plug is a round tube for low-voltage DC. |
Also called
DC barrel plugDC power plug5.5x2.1mm DC plugbarrel jack plugcoaxial power plug
Good to know
The 5.5/2.1 mm size and 8 mm insertion are estimates for the pool-cleaner adapter; its exact size is not established.
Related connections
Design with real parts
Crafti checks which parts connect, right in your browser.