Arizona sand has been used for testing filtration, automotive, and heavy equipment components for decades. A variety of names have been applied to Arizona sand including Arizona Road Dust, Arizona Silica, AC Fine and AC Coarse Test Dusts, SAE Fine and Coarse Test Dusts, J726 Test Dusts, and most recently ISO Ultrafine, ISO Fine, ISO Medium and ISO Coarse Test Dusts. Many military and industrial specifications require use of Arizona Test Dust and refer to one or more of the above names. This report will attempt to describe particle size differences and provide a brief Arizona test dust history dating back to 1940.