The loose lug nut indicators, or "flags", do exactly what the name says. They inform drivers and maintenance when a wheel lug has loosened prematurely. They are installed on a wheel after a bus has traveled at least 100 miles and after the lug nuts are re-torqued. There use to be 2 different colors (yellow and orange). The yellow flags were for S-cam brake systems in which the wheel temperature did get as high as the wedge brake systems. Orange was for wedge brake systems and on some buses, the drive axle.