Milton Industries 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. We were also 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. 1/4 in NPT air inlet.