Designed with a tight collet internal diameter of 9mm, these extensions are perfect for Forstner bits with shank sizes of 3/8 inch or slightly smaller. The ensures a snug fit, enhancing stability and accuracy during drilling. Extend your drilling capabilities with these Forstner drill bit extensions, adding over 3-1/4" and 5-3/4" to your drilling depth. Ideal for deep hole projects in larger vases or containers, these extensions transform standard Forstner bits into more versatile tools. Constructed from high-carbon steel, these extensions are not only robust but also ground and polished for optimal performance. Their durability ensures long-term use, making them a reliable addition to your tool kit. Each extension comes equipped with two set screws and a hex key for secure attachment. Simply use the included hex key to tighten the screws, ensuring your Forstner bit is firmly fixed and ready for precise drilling. Featuring a Round shank diameter of 3/8-inch and total lengths of 4.5 inches and 6.8 inches, these extensions are designed to provide significant additional length, allowing for drilling without the need for equipment., Manufacturer: Akfldms