The 4-1/2” x 7/8” Alpha Disc by Black Hawk Abrasives is one of the biggest, baddest, and best high density flap discs you've ever used. These state of the art 4.5 inch flap discs start with top of the line ceramic abrasive grains. Ceramic grains offer a number of advantageous properties that make them the longest lasting and fastest cutting, but also ideal for use on more sensitive work pieces. First ceramic grains are “self-sharpening”, which means their molecular structure causes them to fracture in a way that continuously produces sharp cutting edges. This characteristic makes these 4.5 ceramic flap discs consistently fast cutting and precise throughout their useful life. Secondly, these ceramic grains have a cool grinding aid which reduces heat buildup during use, simultaneously protecting the work piece and further increasing the life of the flap disc. Lastly, the ceramic grains on the Black Hawk Alpha Flap Discs are “Contaminant Free” meaning they contain less than .1% of iron, sulfur or chlorine. This prevents after rust and corrosion (stainless steel WILL NOT rust as a result of using this flap disc). The 4.5” x 7/8” Alpha Disc continues to set itself apart from the pack with the quantity and quality of the flap material that the ceramic grains are affixed to. As the name implies “Alpha” discs are extra-large flap discs and thus have approximately 30% more sanding flap material than standard 4-1/2” Black Hawk Flap Discs (which are already well above industry average). These additional XL flaps are made of polyester offering the greatest level of strength and durability compared to poly-cotton or cotton varieties. If all of that wasn't enough, the 4 ½ inch Black Hawk “Alpha Disc” features a Hybrid flap layout. This compact design compresses the flaps on the edges to provide greater edge strength and longevity during the toughest grinding applications.