Ethernet Vampire Tap

example:

The typical Ethernet 10Base5 Tap consists of two rectangular sections.  The upper section is a clamping and piercing mechanism through which the long (up to 500 meters) "backbone" cable passes.  The lower section is a powered Transceiver (transmitter and receiver) to which a 15-pin Ethernet AUI (Attachment Unit Interface) connector and cable is attached.  The AUI (ribbon or shielded multipair) cable is not shown in the above illustration, but it would attach to the 15-pin connector that is partially visible at the left side of the Transceiver.

The other end of the AUI cable is the attachment point for an Ethernet devie (i.e. a Hub) or an end node (i.e. computer).  The "vampire" name is a reference to the cable piercing mechanism - usually two "teeth" toward the ends of the clamping section which pierce the coaxial cable's outer cover and make contact with the conductive shield.  These two teeth are electrically identical.  A third tooth, between the outer two teeth, pierces all the way to the central conductor of the coaxial cable and completes the connection between the coaxial Ethernet "Bus" and the Transceiver.