Welding and compressed gas regulator gauge are available in two types; high pressure and low pressure. High pressure is used for tank to measure pressure and how much gas volume left in cylinder,low pressure for down-stream to measure regulated pressure.
OX-A type (bottom mount, for oxygen)
AC-A type (bottom mount, for acetylene)
AP-A type (bottom mount, gold painted case)
welding tank regulator service (low pressure for regulator, high pressure for tank)