. This quick-test style tester does not require threading
  into the spark plug hole, making it an ideal, economic
  solution for quickly diagnosing engine compression
  problems such as worn piston rings, sticking or burnt
  valves, blown head gasket(s), or carbon build-up in
  cylinders, on cars and small engines. Not for use on
  diesel engines.
. This useful quick-test style compression tester features
  a 0-300 psi test gauge and a pressure release plunger
  in the stem.
. Large easy-to-read pressure gauge.
. Universal rubber adapter fits virtually any size spark
  plug hole
. Manual release valve holds peak and pressure readings for
  easy recording
. Small compact unit fits conveniently into toolbox
. Use in vacuum gauge and fuel pump test
. 2-3/4 (70 mm) diameter Bourdon tube gauge readings
  indicated in two (2) scales of measure: kpa & psi with
  pressure release and quick-change coupler, and stem with
  universal rubber spark plug hole adapter and manual
  release pressure valve
. Range: 0 ~ 20 kpa/0 ~ 300 psi
. Included: 1.Compression test gauge
            2.Depressor valve
            3.Universal rubber adapter