United abrasives – sait 22614 depressed center wheel t27 z-tech 7″x 1/4″x 5/8-11″ zirconium grain features: the highest quality zirconium grain all sizes are made with uniform grain throughout, no filler grain used our unique super-lock hub combines both a mechanical locking system and chemical bond providing one of the safest, vibration-free designs in the industry