Trigg Industries brand Air Switch for road tube counters. Field tested in Data Acquisition, GK Instruments, Golden River and Streeter Amet type counters. Properly counts even small vehicles as far as 110 feet from counter. Will not over-count. Solid state, heavy duty, accurate and easy to install. Fully guaranteed for one year. Dimensions 1 15/16" (5 cm) diameter, 1 1/4" (3 cm) body thickness. Call to verify installation for your particular model counter.