The Drill Chuck Arbor is designed to fit into either end of the extension bar. Always use the end which provides the closest fit. The sleeve is only required when using metric Forstner Bits up to 30mm. All other bits can be gripped by insertion into the appropriate (closest fit) end of the extension bar. Specifications: Shank Diameter: 9.5mm or 10mm Overall Length: 185mm (Excl Bit) Material: 12L14 Steel Note: Repeated changing of drill bits will cause damage to the drill shanks making their removal difficult. To avoid this, grind or file a small flat section on the drill shank located where the grub screw will bite