Definition of plug tap in English:

plug tap

noun

Engineering
  • A tap with a flat end and an untapered shank, used for finishing the cutting of an internal thread in a blind hole (also called bottoming tap); (also, chiefly US) a tap with a fairly steep taper for starting a thread.

Origin

Early 19th century; earliest use found in James Smith (1775–1839), writer and humorist.