1/2" to 1/4" Router Bit Collet Extension and Reducer. Extends The Router Bit an Additional 2-1/4" and Accepts 1/4" Shank Router Bits Into the Collet - - Amazon.com
Chiloskit 2 Pics 1/2" to 1/8" Router Collet Chuck Adapter for CNC Lathe Router Milling Bit - - Amazon.com
uxcell Router Collet Driver Adapter Set Convert 8mm/12mm/12.7mm to 6mm 8mm/9.5mm/12.5mm to 6.35mm 10mm/12mm to 8mm 12mm to 10mm for CNC Engraving Bit Machine - - Amazon.com
Adapter Shank Cnc Router Tool Collet Cone 1/2" 1/4" 3/8" Clamp Of 6mm 6.35mm 8mm 12mm For Makita Bosch Hitachi Dewalt Milling - Power Tool Accessories - AliExpress
Amazon.com: 1/4 Inch Shank Router Bit Collet Extension Chuck Converter Adapter, Convert 1/2-Inch & 1/4-Inch Shank Bits with ER20 Spring Collet, ER20 M Type Collet Chuck Wrench Spanner -(Pack of 4) :