3M™ Shaft Mounted Flap Wheel 339. Introducing the 3M™ 339, this flap disc provides a versatile one disc system that features an impressive aluminium oxide abrasive. The 339 flap wheels are long-lasting and precision made to provide you with overall consistency and greater control over a number of critical tasks Excellent for cutting and polishing of metallic components. Run straight onto a right angle grinder, are a one-step system for grinding and blending. The 339 is a wheel with abrasive being resin mounted onto the spindle. Features and Benefits. Fast cutting aluminium oxide abrasive Flexible X-weight backing Spindle mounted Excellent cut and polish capabilities. Typical Applications. These flap wheel brushes are used with power tools. Suitable for light deburring, cleaning, polishing and finishing when preparing metals, woodworking, stone smoothing, and paint or rust removal. FAQ's. How should these wheels be stored . Flap discs should be stored flat, avoiding damp and frost or wide temperature variations. What do Grit sizes mean . P40 Grit – Useful when you need to remove heavy stock from a surface. P60 Grit – For when you need to remove stock from a surface, but will need to refine the finish. P80 Grit – This is for light stock removal and sharping only.