Milescraft 3-Piece Tapered Plug Cutter Set - 1/4-In, 3/8-In, and 1/2-In - Steel Construction - Quick Change Compatible in the Woodworking Tool Accessories department at Lowes.com
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Carbide-Tipped Dowel, Plug & Tenon Cutters - Lee Valley Tools
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Rockler Tapered Plug Cutters with Hex Shanks | Rockler Woodworking and Hardware