Features:Performance-tested and calibrated. Measures in pounds per square inch (PSI, 10-160) and kilopascal (kPa, 80-840, increments of 2-lb.) readings.Makes tire valves more accessible with the two heads for easier access.Heavy-duty construction. Magnifying window lens. Full-swivel chuck. 15-inch hose.Gauge and valve cartridges can both be replaced.This is the first original gauge of this type ever built!Milton specializes in tire inflator gauges and this original S-506 dual chuck inflator gauge was the first gauge of its kind ever built in the industry. The very first in the industry to offer replacement cartridges! Gauge and valve cartridges are both replaceable. This essential pneumatic tool is ideal for any vehicle trunk, home garage, or automotive shop. Dual head chuck inflator gauge is made of heavy duty construction which provides for long life, even under extreme use and conditions. Equipped with magnifying lens for full view of scale.If using a dual head type tire chuck with an inflator gauge and notice air is escaping through the off-side once connected to the tire's Schrader valve, simply release the trigger and remove the inflator from the Schrader/tire valve. Point the straight side of the outlet up into the air (make sure it's not pointed at someone). Squeeze trigger, allow air to flow (gravity will cause the sealing valve to drop), and place the chuck end onto the Schrader/tire valve while air is still flowing. Air will start to flow into the tire.Dual head type tire chucks are unable to inflate a completely flat (zero air pressure) tire. Tire air pressure would normally cause the sealing valve to move and seal the unused side of the chuck. However, if a tire has 0 air pressure, the self-sealing valve has no pressure to react to.