Air-Chex is a bus, truck, tractor, and trailer tire air pressure monitor/verification and maintenance system*. Easily obtain accurate truck or bus dual tire pressures from a few feet away, drastically reducing tire pressure check time or walk-arounds from 20-30 minutes to less than 2 minutes. Airing up the inner dual-tires can be done easily right from Air-Chex's unique triple seal flow thru valve . Save fuel, tire wear and tear, and time. Get extra life from retreads. For 16" - 24" wheels. Will easily pay for itself in only months, and continue to save fuel, labor, and tire wear, maintenance free, year after year. No batteries that die after 9 months, no seals to wear out, and no piggy-backing on compressor systems that were designed exclusively for braking. Air-Chex is easily removed from the permanently attached low profile mounting shoe and does not interfere with tire/wheel service. Extra shoes are supplied to allow Air-Chex to be moved from wheel to wheel quickly.