These flap discs are designed for use with 4 1/2" (115mm) angle grinders and sanders. They are ideal for removing rust, grinding welds, parting lines on casting and carbon steels, and removing rough edges on most surfaces. The high grain adhesion ensures a long life, outlasting conventional sanding discs. No backing disc is required; they fit directly onto an angle grinder. Available in 40, 60, and 80 grit. Features: Size: 4 1/2" (115mm). Aluminium Oxide backing pad. Lasts up to 25 times longer than a regular sanding disc. 40 grit. Pack of 20.