1 inch 20mm Brass Ring Adapter Reducer Bushing Diamond Saw Blades FITS STIHL SAW | eBay
Winbyoan Saw Blade Bushing Set Saw Blade Adapter Ring, 1 Inch to 20 mm, 1 Inch to 5/8 Inch, 7/8 Inch to 5/8 Inch, 20 mmto 5/8 Inch, 5/8 Inch to 1/2 Inch, Pack of 10 - Amazon.com
EDiamondTools 12 in. General Purpose Segmented Diamond Saw Blades for Concrete and Masonry, 12mm Segment Height, 1 in./20mm Arbor GP12X - The Home Depot
Freud BL71MNA9 1" OD X 20mm ID Saw Blade Arbor Bushing