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Network Connector Types Explained (RJ45, RJ11, BNC, F, Fiber)

Here's how to tell apart the connectors you'll actually run into on cables and wall jacks.

RJ45: the everyday ethernet connector

RJ45 is the clear plastic connector with eight side-by-side pins (8P8C) found on both ends of an ethernet cable, connecting computers, routers, and switches. The connector shape looks the same regardless of cable category (Cat5e, Cat6, etc.), and it snaps into place with a small latch that must be pressed to remove it.

RJ11: the older phone-line connector

RJ11 is a narrower connector used for telephone lines, older landline phones, and some older DSL modems. It's noticeably smaller than RJ45 and usually has 4 to 6 pin slots, though often only the middle 2 to 4 are actually wired. Forcing one into an RJ45 port can damage the port or the connector.

BNC: twist-lock connector for coax

BNC connectors attach to coaxial cable and lock in place with a quarter-turn twist (a bayonet mount), unlike the snap-in RJ45. They were used in early Ethernet wiring (10BASE2) decades ago, and today show up mainly on analog CCTV cameras, broadcast equipment, and test instruments rather than home networks.

F connector: the screw-on coax connector

F connectors have a thin center pin sticking out and screw on by hand, rather than snapping or twisting. They're the standard connector for cable TV and cable internet drops, as well as satellite and shared antenna wiring. Their look is different enough from ethernet or phone connectors that they're easy to identify.

Fiber connectors (SC, LC, and others)

Fiber-optic cable carries signal as light rather than electricity, so it uses connectors built for that job instead of RJ45. The square-bodied SC connector and the smaller LC connector are the most common. In homes, these typically appear only at the point where a fiber line reaches the optical network terminal (ONT); homeowners rarely handle them directly.

How to tell them apart at a glance

RJ45 and RJ11 are the pair most people confuse, but placed side by side, RJ45 is visibly wider with more pins. Coax connectors (BNC, F) are cylindrical rather than rectangular, so they're rarely mistaken for ethernet or phone connectors in the first place.

Connector shape and cable category are different things

An RJ45 connector looks identical whether it's crimped onto Cat5e or Cat6 cable -- the connector shape alone can't tell you the cable's rated speed. To find that out, check the category printed along the cable's outer jacket rather than judging by the plug.

Common mistakes to avoid

A common mistake is forcing a phone-line RJ11 plug into an ethernet RJ45 port -- it may seem to fit, but it can damage the port's internal contacts or the connector's latch. In older buildings where phone and coax jacks sit side by side on the same wall plate, it's also easy to mix up which jack serves which purpose when rewiring.

Inside an RJ45 plug: T568A and T568B wiring

Crimping an RJ45 connector isn't just about pushing eight wires into eight slots in any order -- the wires inside must follow a standard color sequence, most commonly T568B (or T568A). Both ends of a cable need to follow the same standard, or the connection won't carry a reliable signal even though the connector looks correctly attached.

Some RJ45 ports carry power as well as data

Certain ethernet ports use Power over Ethernet (PoE) to send electrical power through the same RJ45 cable that carries data, letting devices like security cameras or wireless access points run without a separate power cable. Not every port supports this, so it's worth checking a device's specifications before assuming a single cable will handle both.

Frequently Asked Questions

Is it okay to accidentally plug an RJ11 connector into an RJ45 port?

RJ11 is narrow enough to physically slide partway into an RJ45 port, but it isn't designed to lock in properly, so the connection is unreliable, and forcing it can damage the port's internal contacts or the connector's latch. Since the two serve entirely different purposes, it's best to only connect each cable to its intended port.

Can I terminate a fiber-optic connector myself at home?

Fiber requires precise alignment and cleaving equipment that most people don't have, so it's not a practical DIY job. Fiber internet installations are typically completed by a technician who runs the connection to the optical network terminal (ONT); anything after that point is usually a standard ethernet (RJ45) cable that a homeowner can handle.