Specifications
| Outside diameter | 7.9 mm |
|---|---|
| Hole diameter | 5.5 mm |
| Centre pin in the hole | yes |
| Standard | de facto size |
| Rating (catalogue part) | no published rating |
| Polarity | not set by the size: read the symbol |
Lookalikes and how to tell them apart
A little thicker than the Dell and HP 7.4 × 5.0, which also has a centre pin: measure the hole too, 5.5 against 5.0 mm. Sources give this plug’s outside as anything from 7.5 to 8.0 mm, and the ThinkPad reads its pin to identify the adapter.
| Size | Centre pin | Standard |
|---|---|---|
| 7.9 × 5.5 mm | yes | de facto size |
| 7.4 × 5.0 mm | yes | de facto size |
Before you plug it in
Measure with a caliper: the metal sleeve gives the outside diameter. For the hole, use drill bits as gauges: the largest one that slides in gives the size. If there is a pin in the middle, a bit won’t go in: use the caliper’s inside jaws.
The size says nothing about polarity: look for the symbol (a dot inside a C, with + and −) on the device and on the adapter. Centre positive is the most common.
Laptop plugs with a thin centre pin (Dell, HP, Lenovo ThinkPad) use it to identify the adapter: a copy without that line may run the laptop but refuse to charge it.
Open the connector identifier →Not sure it is this size? Enter the outside and hole diameters: the identifier compares 22 DC plug sizes.
Other DC plug sizes
2.0 × 0.6 mm 2.35 × 0.7 mm 2.5 × 0.7 mm 3.0 × 1.1 mm 3.5 × 1.1 mm 3.5 × 1.35 mm 4.0 × 1.35 mm 4.0 × 1.7 mm 4.5 × 3.0 mm 4.75 × 1.7 mm 4.8 × 1.7 mm 5.5 × 1.7 mm 5.5 × 2.1 mm 5.5 × 2.5 mm 5.5 × 3.0 mm 5.5 × 3.3 mm 6.3 × 3.0 mm 6.5 × 4.4 mm 7.4 × 5.0 mm
All DC plug sizes, with a chart →
Frequently asked questions
Is 7.9 × 5.5 mm a standard size?
No: it is a de facto size, common but not set by IEC or EIAJ. Check the voltage and polarity on the label.
Sizes and ratings from the makers’ catalogues (Same Sky, Lumberg, Switchcraft) and the EIAJ and IEC summaries. A plug’s rating is a maximum: the adapter’s label says what it actually supplies.