Our salvaged Lonergan brass pressure gauge was designed to measure both exhaust pressure and vacuum on a scale from 0 to 30 either way. The undamaged glass on the top of the dial measures about 5 1/4 inches in diameter. The main brass housing measures about 7 1/2 inches in diameter. The gauge has has three mounting holes. The connection point for the source being measured is on the back of the gauge. When mounted to the wall, this pressure gauge will extend out from the mounting surface by about 2 3/4 inches.  The surface on the back of the gauge is not brass and is painted black. This salvaged Lonergan brass pressure gauge weighs just over 6 pounds.