USB 3.0 A to B Cable: Recognising the 3.0 B Connector
The B connector grew taller when USB 3 arrived. That extra height is the only visual difference between a 2.0 printer cable and a 3.0 printer cable, and it is the difference between 480 Mbps and 5 Gbps.
Quick Answer
A USB 3.0 A to B cable connects a host port to a device with a square B socket: printers, scanners, docking stations, external drive enclosures and some audio interfaces. The 3.0 B plug is taller than the 2.0 version because it carries nine contacts instead of four. It negotiates up to 5 Gbps, and it fits USB 2.0 B sockets without damage.
Telling the Two B Plugs Apart
| Feature | USB 2.0 B | USB 3.0 B |
|---|---|---|
| Height of shell | About 11 mm | About 16 mm |
| Contacts | 4 | 9 |
| Rate | 480 Mbps | 5 Gbps |
| Common colour | Black or grey | Often blue insert |
| Fits the other socket | Fits 3.0 sockets | Only fits 3.0 sockets |
Why the Extra Contacts Exist
SuperSpeed pairs
Two additional differential pairs carry the high speed link in both directions, separate from the original pair used for compatibility and control.
Backwards behaviour
The 2.0 pair keeps working, so a 3.0 cable on a 2.0 port behaves exactly like a 2.0 cable. Nothing is lost except the rate.
One direction of fit
A 3.0 B plug will not enter a 2.0 B socket: it is physically too tall. Check the socket before ordering replacements for a mixed fleet.
Devices That Use It
| Device | Typical rate needed | Notes |
|---|---|---|
| Office laser printer | 480 Mbps is plenty | A 2.0 cable is normally sufficient |
| Document scanner | 5 Gbps useful | High resolution scans arrive faster |
| External drive enclosure | 5 Gbps | Mechanical drive limited near 150 MB/s |
| Audio interface | 5 Gbps or 10 Gbps | Channel count and sample rate drive the need |
| Docking station | 5 Gbps or higher | Shared across display, Ethernet and USB ports |
Real-World Applications
- Replacing a scanner cable to cut scan to file time.
- Standardising the printer fleet on a documented cable type.
- Connecting a drive enclosure that only offers a B socket.
- Keeping a spare in the IT cupboard for dock replacements.
Ordering Checklist
- Confirm the device socket is the tall 3.0 B shape.
- Confirm the host port generation.
- Choose a SuperSpeed rated cable, not a look-alike.
- Keep the length under about 3 m for a reliable 5 Gbps link.
- Label the cable so it is not mixed up with a 2.0 printer cable.
Related Guides
For the wider connector family, read USB to USB 3 cable. For the port label, see SS10 USB. For drive enclosures and transfers, start with USB 3.0 data transfer cable.
FAQ
Will a USB 2.0 A to B cable work in a USB 3.0 printer?
Yes, at USB 2.0 speed. Printers rarely need more, so a 2.0 cable is usually adequate.
Why does my USB 3.0 B cable not fit the socket?
The socket is a 2.0 B socket, which is shorter. The 3.0 plug cannot enter it.
Are all blue A to B cables USB 3.0?
No. Colour is a convention. Check the plug height and the stated rating.
How long can a USB 3.0 A to B cable be?
About 3 m for reliable 5 Gbps operation. Longer runs need an active cable or an extension with a repeater.