The Free On-line Dictionary of Computing (30 December 2018):

vampire tap

    A device to connect a network node to
   an RG8 thick ethernet cable without affecting other
   connected nodes.

   A vampire tap has an interface box with a "V" shaped groove
   along one side.  A sharp needle protrudes from the center of
   the groove.  The cable is clamped into the groove by a grooved
   plate held in position by two thumb screws.  With sufficient
   practise, tightening the screws forces the needle through the
   cable jacket and into contact with the cable's center wire
   while other spikes bite into the outer conductor.  The
   interface box has a 15 pin connector to connect to the network
   node.

   The vampire tap is often built into the transceiver, with a
   more flexible multi-wire "drop cable" to connect the
   transceiver to the node.

   (2004-08-25)