All Balls seal heads are made from 6061-T6 Aluminium to save weight. All Rear Shock Seal Kits have an air bleed hole. This helps remove air from the oil reservoir during seal head installation. The oil seal utilizes a double lip design and a low friction elastomer. This gives the seal head additional dirt exclusion and yet maintains a low drag (low friction) seal. The dust seal utilizes a spring type exclusion seal to maintain constant pressure and assure good dirt and contaminant exclusion over the life of the seal head. On early Yamaha seal heads All Balls have done away with the multi piece design. This makes installation quicker and easier.Quality design and construction of every All Balls piece meets the toughest standards and conditions - from daily commuting to full-on racing, all older bearing and seal designs are upgraded to the best and latest specs and designs. All seal heads are made from 6061-T6 Aluminium to save weight. They also feature an air bleed hole & a spring type exclusion seal to maintain constant pressure & assure good dirt & contaminant exclusion over the life of the seal head.