Square Hole Drill Bit Adapter for Easy Installation and Disassembly - Mortising Attachment for Drill Press, Mortise Machine Power Tool Accessory for Drill Machines - Walmart.com
Drill bit cuts a square hole - Boing Boing
Square Hole Mortising Drill Bit - Not sold in stores
Square Hole Drill Bit Adapter Clamp Adjustable from 1.5-2.2inch Stainless Steel Bench Drill Press Converter for Drill Machine Accessory Full set - Walmart.com
Square Hole Mortise Chisel Drill Bit Tools, HSS Woodworking Hole Saw Mortising Chisel Drill Bit Set Twist Drill, Different Sizes 1/4" 5/16" 3/8" 1/2" 9/16" 5/8"(6pcs) - Amazon.com