Thick Coaxial Cable (10Base5 / Thick Ethernet / ThickWire / ThickNet, Yellow Cable, Thick Coax) Thick Ethernet Cable: A transmission medium specified by IEEE 802.3 that carries information at rates up to 10Mbps in baseband form using 50 ohm coaxial cable over distances up to 500 meters (1,640 ft). Thick Ethernet cable is typically used as a trunk or backbone path of the network.

Thicknet cable (also known as Standard Ethernet) is relatively rigid, being 0.5 inches in diameter. The IEEE specification refers to this type of cable as 10Base5, referring to its main specifications of 10 Mbps data rate, baseband transmission type, and 500 metre maximum segment length. Thicknet is generally used to provide the network backbone and can support up to 100 nodes per backbone segment.

A tranceiver is connected to the cable using a "vampire tap", so called because it clamps onto the cable, forcing a spike through the outer shielding to make contact with the inner conductor, while other spikes bite into the outer conductor. 10base5 cable is designed to allow transceivers to be added while existing connections are live. A cable with AUI (Attachment Unit Interface - also known as DB-15) connectors at each end is used to connect the tranceiver to the network nodes adapter card. The drop cables are typically 3/8-inch shielded twisted pair (STP) cables and can be up to 50 metres (164 feet) in length. The minimum cable length between connections (or taps) on a Thicknet cable segment is 2.5 meters (about 8 feet). Thicknet cable has a data rate of 10 Mbps and can carry a signal for 500 meters before a repeater is required. A maximum of five backbone segments can be connected using repeaters (based on the IEEE 802.3 specification).

The grade of coaxial cable used will depend on where it is used. Normal PVC coaxial cable is flexible, easy to work with, and may be used in exposed areas of offices, but because it gives of poisonous fumes when it burns, it is against the fire regulations in many countries for it to be installed in floor and ceiling voids which are also used to allow air to circulate around the building.

Thick coax was the transmission medium originally used by Xerox for their Ethernet network, although it was later superceded by thin coax. Although still used in many networks, coaxial cable is gradually being replaced by fibre optic and UTP cable - fibre optic is normally used for the network backbone, with UTP being used to connect workstations to hubs or MSAUs.