3M 36258 321U Series Abrasive Disc, 5 in Dia, 240 Grit, Hook and Loop, Blue

Our 3M™ Hookit™ blue abrasive disc 321U delivers best in class performance at every stage of paint prep and body repair. Premium aluminum oxide mineral abrasive is blended with ceramic grain for a full range of automotive sanding applications. Our multi-hole discs feature a specially-designed pattern that reduces loading, extends disc life and aligns with most backup pads. Hookit™ attachment makes disc changes easy.
3M Hookit coated 321U hook & loop disc uses ceramic aluminum oxide as the abrasive material and has a diameter of 5 in. 3M incorporates this ceramic aluminum oxide material into the hook & loop disc forming a grit of 240. This item is on a paper backing, C weight.
Specifications:

Abrasive Type: Coated

Specification parameters description:

Abrasive Material:
Values: A/O Aluminum Oxide AO A/Z Alumina Zirconia AZ S/C Silicon Carbide SC Aluminum Oxide Aluminum oxide is an artificial abrasive suited for general purpose stock removal and finishing. It is the mostly commonly used abrasive and can be used for most steels and ferrous alloys. Aluminum oxide is slightly softer but tougher than silicon carbide. Ceramic Ceramic is used for aggressive cutting and grinding of stainless steel, titanium, and metal alloys. The abrasive grain is designed to fracture during use so that it maintains sharpness. Ceramic Aluminum Oxide Cerium Oxide Cerium oxide is used for fine polishing and lapping of glass, gemstones, optical mirrors, and lenses. It should be used wet or in slurry form. Diamond Diamond can be either natural or manufactured and is one of the hardest abrasive materials. It is commonly used for grinding and polishing stone and very hard steels, and for sharpening other cutting tools. Nylon Silicon Carbide Silicon carbide is a manufactured material that is extremely hard but brittle. It is commonly used for fast cutting under light pressure, particularly on cast iron, nonferrous metals, and materials such as glass and plastic. Precision Shaped Ceramic Grain Zirconia
Grit:
Grit is a measurement of the size of abrasive particles embedded in coated abrasives. The most common standards for grit size are the United States CAMI (Coated Abrasive Manufacturers Institute) and the European FEPA (Federation of European Producers of Abrasives). A smaller grit number means larger particles and a coarser grade, while high number grits are used for finer work. Grit is generally a unitless measure but is sometimes measured in microns.
Backing Weight:
Paper and cloth have a lettering scale for backing weight that measures strength of the material onto which the abrasive is mounted. Paper uses the letters A-F, where A is a lighter weight and most flexible and F represents a rigid, heavier backing. Lighter backings are typically paired with finer abrasive grits, suitable for blending and finishing. Coarser grits used for deburring and stock removal rely on a heavier backing. Cloth uses a lettering system of J, X, and Y for backing weight. J weight (jeans) is the lightest and most flexible, X weight (drills) is more durable and recommended for medium duty work, and Y weight is the toughest and least flexible. Fiber backings are made from chemically-impregnated paper to form a very hard, strong backing material. Fiber is used primarily for sanding discs. Polyester film backing provides high strength with a very thin backing and is used for very fine grits. It is more tear resistant than paper backing and is also waterproof.