Use this to sharpen your dull 28mm straight rotary blades.
Omnigrid Rotary Replacement Blades 6 - Pack, 28 mm - Yahoo Shopping
Martelli Enterprises Ergo Replacemnt Blade 60mm 10ct - 123Stitch
Colonial Needle Rotary Mat Smoother : Target
Colonial Needle 60 mm Rotary Blade Sharpener : Patio, Lawn & Garden
Rotary Blade Sharpener Replacement Disk 28mm Colonial 5790TS-R28 - OzQuilts
Olfa RB28-2 28MM Rotary Blade 2ct - 123Stitch
Sew Easy ~ The Sewing Shop
Colonial Dual Rotary Blade Sharpener 45mm
Colonial Dual Rotary Blade Sharpener 45mm
Dual Rotary Blade Sharpener/60mm Sharpener/twist N' Sharpen/restore Sharp Edge to Your Rotary Blades/3272