The Items of the Usual class are so common that they appears on most bloons of the same kind. (For example: Ores and Rubber are all Usual Items, each Ore appears after you pop pretty much any bloon of that kind.) Items crafted from this class of material often requires a ridiculous amount of Usual Items to craft. (For example: an Auracryst needs as much as 750 Aurae Dusts!)