USB B to USB B Cable: Uncommon, Specific and Easy to Misuse
The square B connector is most familiar as the printer end of a cable. A B to B cable has that plug at both ends, which makes it useful in a narrow set of situations and dangerous in a few others.
Quick Answer
A USB B to USB B cable connects a device or hub with a downstream B socket to a host with a B socket, most often a KVM switch, an upstream hub port or a MIDI interface. Both ends are square B plugs, in USB 2.0 four pin or USB 3.0 nine pin form. It should never be used as a substitute for a computer to computer cable.
Where B to B Is Used
| Application | How it is used | Notes |
|---|---|---|
| KVM switch | Connects the switch to the computer | Very common use |
| USB hub upstream | Some powered hubs present a B socket upstream | Check whether the hub expects A or B upstream |
| MIDI and audio interfaces | Rack interfaces with a B socket | Often B to A in practice |
| Industrial controllers | Programmer or configuration port | Verify the socket type |
| Some older printers and plotters | Device to device links | Unusual, check the manual |
B Plug Versions Again
USB 2.0 B
Four pins, about 11 mm tall, 480 Mbps. The standard printer plug.
USB 3.0 B
Nine pins, about 16 mm tall, 5 Gbps. It will not fit a 2.0 socket.
Mixing them
A 2.0 B plug fits both sockets. A 3.0 B plug fits only the taller socket, so a mixed installation needs both cable types on hand.
What Not to Do
- Do not connect two computers with any B to B cable.
- Do not use an A to A cable to join two hosts.
- Do not force a 3.0 B plug into a 2.0 socket.
- Do not assume a B socket means the device is a peripheral you can attach to a laptop.
Real-World Applications
- Wiring a KVM switch into a desktop and a laptop.
- Connecting a rack MIDI interface with a B socket.
- Replacing a missing upstream cable for a powered hub.
- Servicing industrial equipment with a B configuration port.
Buying Checklist
- Confirm both sockets are B type and note the height.
- Decide between 2.0 and 3.0 based on the sockets.
- Choose the length for the physical layout, keeping 3.0 runs short.
- Check the device manual for the supported upstream connection.
- Label the cable, since it is easily confused with a printer cable.
Related Guides
For adapter selection on modern hosts, read USB-C to USB 2.0. For the Mini connector family, see Mini USB adapter. For compact port expansion, start with 4 port mini USB hub.
FAQ
Can I use a B to B cable to transfer files between two PCs?
No. Both ends are hosts and the cable has no arbitration. Use a bridging cable or a network.
Is a B to B cable the same as a printer cable?
No. A printer cable is A to B. B to B has the square plug at both ends.
Will a USB 3.0 B to B cable fit my KVM?
Only if the KVM sockets are the taller 3.0 B type. Most KVMs use 2.0 B.
Why is this cable harder to find?
It has fewer applications than A to B, so fewer vendors stock it.