This is a 50 pak of 5" Hook and Loop 180 grit sanding disc.  Blue Film is changing the industry. Blue Film is made on a 5 mil PET film base using PREMIUM Aluminum oxide grain. It has non loading, and grinding aids in the resin, that provides excellent life and durability. The Blue Film is an outstanding product for many disc applications. Great for automotive, wood, metal, corian, fiber glass and many other disc sanding applications.   They will fit any 5" sander with the 8 hole pattern.