The Pferd Polifan SG aluminum oxide abrasive type 29 flap disc has a phenolic resin backing for reinforcement and a threaded hole for attachment to grinding tools. Aluminum oxide is the most common abrasive grain and is suitable for grinding steel, stainless steel, plastic, and wood. It is free of iron, sulphur, and chlorinated fillers. Applications include surface and edge grinding. The disc has an angled shape for maximum workpiece contact and is commonly used with angle grinders. Threaded hole fastening type indicates a disc with a female-threaded central hole that twists onto a threaded arbor. Abrasive flap discs are made from overlapping pieces of coated abrasive attached to a hub. They help reduce finishing time and cost by grinding and finishing in the same step, such as when removing a weld bead and smoothing the workpiece around the weld. Flap discs are coated, meaning an adhesive is used to attach the abrasive grains to a backing of paper, plastic, or cloth. The action of a flap disc is much like that of a sanding disc: the grinding or polishing occurs on the face of the disc. They are used for a variety of applications from shaping a part to fine finishing, depending on the grit size. Low grit numbers like 40 are coarse (with fewer, larger grains) and remove excess material and shape parts. High grit numbers like 400 are fine (with more, smaller grains) and help create a smooth surface finish. Pferd manufactures abrasives and cutting tools for grinding, finishing, and cutting. Founded in 1799 in Germany, Pferd has its U.S. headquarters in Leominster, MA, and meets International Organization for Standardization (ISO) 9001 standards.